Remove pointless msvs_cygwin_shell:1

In a mac-only block. Should probably also be 'copies' but
I don't have a mac build handy to test on.

TBR=thakis@chromium.org
BUG=123026

Review URL: https://codereview.chromium.org/134483011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245818 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245818