Remove cygwin_shell usage for cp in chrome_exe.gypi

TBR=zturner@chromium.org
BUG=123026

Review URL: https://codereview.chromium.org/93683002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245751 0039d316-1c4b-4281-b951-d872f2087c98
Automated Commit: Committing new LKGM version 5251.0.0 for chromeos.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245752 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245752