Remove build[41..48]-b4 from linux_gpu on master.tryserver.chromium.gpu.
Remove build[41..48]-b4 from linux_gpu on master.tryserver.chromium.gpu.

Returning these physical builders to the machine pool.

BUG=360364

Review URL: https://codereview.chromium.org/239343016

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@264549 0039d316-1c4b-4281-b951-d872f2087c98

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