Revert version checking code

Checking version with `hlexists()` does not work as expected.

after/syntax/css/css-display-3.vim

@@ -1,6 +1,5 @@
-if !hlexists('cssDisplayProp')
-  syn match cssFontProp contained "\<display-\(inside\|outside\|extras\|box\)\>"
-  syn keyword cssFontAttr contained contents
-  syn match cssFontAttr contained "\<\(block\|inline\)-level\>"
-  syn match cssFontAttr contained "\<inline-list-item\>"
-endif
+" TODO: create cssDisplayProp group and cssDisplayAttr group
+syn match cssFontProp contained "\<display-\(inside\|outside\|extras\|box\)\>"
+syn keyword cssFontAttr contained contents
+syn match cssFontAttr contained "\<\(block\|inline\)-level\>"
+syn match cssFontAttr contained "\<inline-list-item\>"

after/syntax/css/css-shapes-1.vim

@@ -1,5 +1,4 @@
-if !hlexists('cssShapesProp')
-  syn match cssFontProp contained "\<shape-\(outside\|image-threshold\|margin\)\>"
-  syn match cssFontAttr contained "\<margin-box\>"
-  syn region cssFunction contained matchgroup=cssFunctionName start="\<\(inset\|circle\|ellipse\|polygon\)\s*(" end=")" oneline keepend
-endif
+" TODO: create cssShapesProp group and cssShapesAttr group
+syn match cssFontProp contained "\<shape-\(outside\|image-threshold\|margin\)\>"
+syn match cssFontAttr contained "\<margin-box\>"
+syn region cssFunction contained matchgroup=cssFunctionName start="\<\(inset\|circle\|ellipse\|polygon\)\s*(" end=")" oneline keepend

after/syntax/css/css-writing-modes-3.vim

@@ -1,8 +1,7 @@
-if !hlexists('cssWritingModeProp')
-  syn match cssFontProp contained "\<text-\(orientation\|combine-horizontal\)\>"
-  syn match cssFontProp contained "\<writing-mode\>"
-  syn keyword cssFontAttr contained before after mixed isolate plaintext
-  syn match cssFontAttr contained "\<\(upright\|sideways\(-right\|-left\)\=\|use-glyph-orientation\)\>"
-  syn match cssFontAttr contained "\<isolate-override\>"
-  syn match cssFontAttr contained "\<\(horizontal-tb\|vertical-\(rl\|lr\)\)\>"
-endif
+" TODO: create cssWritingModesProp group and cssWritingModesAttr group
+syn match cssFontProp contained "\<text-\(orientation\|combine-horizontal\)\>"
+syn match cssFontProp contained "\<writing-mode\>"
+syn keyword cssFontAttr contained before after mixed isolate plaintext
+syn match cssFontAttr contained "\<\(upright\|sideways\(-right\|-left\)\=\|use-glyph-orientation\)\>"
+syn match cssFontAttr contained "\<isolate-override\>"
+syn match cssFontAttr contained "\<\(horizontal-tb\|vertical-\(rl\|lr\)\)\>"

after/syntax/css/css3-break.vim

@@ -1,5 +1,4 @@
-if !hlexists('cssBreakProp')
-  syn match cssFontProp contained "\<break-\(after\|before\|inside\)\>"
-  syn match cssFontProp contained "\<box-decoration-break\>"
-  syn keyword cssFontAttr contained any
-endif
+" TODO: create cssBreakProp group and cssBreakAttr group
+syn match cssFontProp contained "\<break-\(after\|before\|inside\)\>"
+syn match cssFontProp contained "\<box-decoration-break\>"
+syn keyword cssFontAttr contained any

after/syntax/css/css3-regions.vim

@@ -1,7 +1,6 @@
-if !hlexists('cssRegionsProp')
-  syn match cssFontProp contained "\<flow-\(into\|from\)\>"
-  syn match cssFontProp contained "\<region-fragment\>"
-  syn keyword cssFontAttr contained element content break
-  syn match cssFontAttr contained "\<\(avoid-\)\=region\>"
-  syn keyword cssPseudoClassId contained region
-endif
+" TODO: create cssRegionsProp group and cssRegionsAttr group
+syn match cssFontProp contained "\<flow-\(into\|from\)\>"
+syn match cssFontProp contained "\<region-fragment\>"
+syn keyword cssFontAttr contained element content break
+syn match cssFontAttr contained "\<\(avoid-\)\=region\>"
+syn keyword cssPseudoClassId contained region

after/syntax/css/css3-transitions.vim

@@ -1,7 +1,6 @@
-if !hlexists('cssTransitionProp')
-  syn match cssFontProp contained "\<transition\(-\(property\|duration\|timing-function\|delay\)\)\=\>"
-  syn keyword cssFontAttr contained linear
-  syn match cssFontAttr contained "\<ease\(-\(in\|out\|in-out\)\)\=\>"
-  syn match cssFontAttr contained "\<step-\(start\|end\)\>"
-  syn region cssFunction contained matchgroup=cssFunctionName start="\<\(steps\|cubic-bezier\)\s*(" end=")" oneline keepend
-endif
+" TODO: create cssTransitionsProp group and cssTransitionsAttr group
+syn match cssFontProp contained "\<transition\(-\(property\|duration\|timing-function\|delay\)\)\=\>"
+syn keyword cssFontAttr contained linear
+syn match cssFontAttr contained "\<ease\(-\(in\|out\|in-out\)\)\=\>"
+syn match cssFontAttr contained "\<step-\(start\|end\)\>"
+syn region cssFunction contained matchgroup=cssFunctionName start="\<\(steps\|cubic-bezier\)\s*(" end=")" oneline keepend