Remove executable bit from files which aren't executable

This has already been done for web-platform-tests, so we shouldn't
get the executable bits back on future imports for those tests:
https://github.com/w3c/web-platform-tests/commit/35c13df5fedbd68dbec5dbb5717cb2f2b2011041

Done using svn propdel svn:executable and commited manually.

BUG=none

Review URL: https://codereview.chromium.org/68773002/


git-svn-id: svn://svn.chromium.org/blink/trunk@161916 bbb929c8-8fbe-4397-9dbb-9b2b20218538