Remove Mac 10.8 x86 Perf expectations

Remove Mac 10.8 x86 Perf expectations

This is one of the problems with the way the RecreateSKPs bot determines which trybots to run: Rather than use a hard-coded list, it figures out which bots have perf expectations and then runs those bots to generate new expectations.  This is problematic when we remove a bot because we have to remove its expectations as well.  This is really not that different from maintaining a hard-coded list...

NOTRY=true
BUG=skia:
R=bensong@google.com, rmistry@google.com

Author: borenet@google.com

Review URL: https://codereview.chromium.org/443093002