Remove now unnecessary msvs_cygwin_shell:1

Was probably necessary for VS builds, but we don't need it any more.

BUG=123026
R=gab@chromium.org
TEST=remove chrome.7z and setup.ex_ and ninja -C out\Debug setup.ex_

Review URL: https://codereview.chromium.org/142343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246103 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246103