gyp: Cleanup dependency on re2.

- Stop always depending on it in xwalk_application_common.gypi, as it is
  only needed for Tizen.

- Remove dependency in xwalk_application.gypi now that the manifest
  handling files are in application/common/ and thus covered by
  xwalk_application_common.gypi.
Merge pull request #2676 from rakuco/gyp-cleanup-re2-dependency

gyp: Cleanup dependency on re2.