Remove unused NSS dependencies in mac certificate handling code. 
Needed to avoid compile error when compiling for mac with OpenSSL.

BUG=None
TEST=None

Review URL: https://codereview.chromium.org/179363006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254455 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254455