Remove unreliable XML entity handling from XML syntax

runtime/syntax/xml.yaml

@@ -10,8 +10,6 @@ rules:
         end: "[/]?>"
         rules: []
     - comment: "<!--.+?-->"
-    # next line for highlighting of character entities doesn’t work as of now
-    - special: "&(#[[:digit:]]{1,4}|#x[[:xdigit:]]{1,4}|[^[[:space:]]]+);"
     - symbol.tag:
         start: "<\\??"
         end: "\\??>"