Remove features deprecated in previous versions

test/lsp/test_lsp_command_formatting.vader

@@ -24,8 +24,8 @@ Execute(Command formatting should be applied correctly for LSP linters):
   \ bufnr(''),
   \ {
   \   'name': 'linter',
-  \   'language_callback': {-> 'x'},
-  \   'project_root_callback': {-> '/foo/bar'},
+  \   'language': {-> 'x'},
+  \   'project_root': {-> '/foo/bar'},
   \   'lsp': 'stdio',
   \   'executable': has('win32') ? 'cmd': 'true',
   \   'command': '%e --foo',