Remove a duplicate include of about_welcome_android.css

Due to flattenhtml="true" we were including 8 copies of the holo_logo.

BUG=326023
TBR=thestig

Review URL: https://codereview.chromium.org/182213002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253987 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253987