Drop build131-m1 from WHITELIST in slaves_cfg_test.py
Drop build131-m1 from WHITELIST in slaves_cfg_test.py

After r295363 it's only used once.

BUG=490866

Review URL: https://codereview.chromium.org/1148733003

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@295366 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build