Revert "highlight: skip processing the same hi group twice"

This reverts commit feee9bcf3c.

It brakes CI and shouldn't be needed

autoload/airline/highlighter.vim

@@ -84,10 +84,6 @@ function! airline#highlighter#exec(group, colors)
   if len(colors) == 4
     call add(colors, '')
   endif
-  if has_key(g:airline_theme_dict, 'a:group') &&
-        \ get(g:airline_theme_dict[a:group]) == a:colors
-    return
-  endif
   if g:airline_gui_mode ==# 'gui'
     let new_hi = [colors[0], colors[1], '', '', colors[4]]
   else
@@ -102,7 +98,6 @@ function! airline#highlighter#exec(group, colors)
         \ s:Get(colors, 4, 'term=', ''))
     exe cmd
   endif
-  let g:airline_theme_dict[a:group] = a:colors
 endfunction
 
 function! s:CheckDefined(colors)
@@ -165,7 +160,6 @@ function! airline#highlighter#load_theme()
   if pumvisible()
     return
   endif
-  let g:airline_theme_dict = {}
   for winnr in filter(range(1, winnr('$')), 'v:val != winnr()')
     call airline#highlighter#highlight_modified_inactive(winbufnr(winnr))
   endfor
@@ -175,7 +169,6 @@ function! airline#highlighter#load_theme()
   else
     call airline#highlighter#highlight(['normal'])
   endif
-  unlet g:airline_theme_dict
 endfunction
 
 function! airline#highlighter#add_separator(from, to, inverse)