Revert r136547 "Enforce VS2010 on trunk."

This is not necessary on trunk.

TBR=kerz@chromium.org

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10382126

git-svn-id: http://src.chromium.org/svn/trunk/src/build@136548 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

gyp_chromium

@@ -107,8 +107,6 @@ if __name__ == '__main__':
     psyco.profile()
     print "Enabled Psyco JIT."
 
-  os.environ['GYP_MSVS_VERSION'] = '2010'
-
   # Fall back on hermetic python if we happen to get run under cygwin.
   # TODO(bradnelson): take this out once this issue is fixed:
   #    http://code.google.com/p/gyp/issues/detail?id=177