Delete AltErrorPageResourceFetcher.  This is no longer being used
as of revision 244611 (https://codereview.chromium.org/67283002/),
I just forgot to delete it in that CL.

TBR=darin@chromium.org
BUG=308232

Review URL: https://codereview.chromium.org/141263002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247276 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247276