Synchronize FeatureDefines.xcconfig

Source/JavaScriptCore:

* Configurations/FeatureDefines.xcconfig: Remove
ENABLE_LINK_PRERENDER.  This was missed in r150356.

Source/WebKit/mac:

* Configurations/FeatureDefines.xcconfig: Add a newline to the
end of the file.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150367 268f45cc-cd09-0410-ab3c-d52691b4dbfc