Simplify makegrammar.pl
    
This change removes the preprocessor and defines parameters from
makegrammar.pl that were passed by gyp but didn't change the output of
the script. This is because we don't have ENABLE in CSSGrammar.y.in.
    
While touching the code, also greatly simplified the script based on
the fact that only one code path was ever used (we only call the
script on CSSGrammar.y.in).
    
CSSGrammar.y is the same before and after this change.

Review URL: https://chromiumcodereview.appspot.com/19792008

git-svn-id: svn://svn.chromium.org/blink/trunk@154700 bbb929c8-8fbe-4397-9dbb-9b2b20218538