Remove bazel-toolchains from gitsync.
Its source of truth is GitHub and thus there's no point in mirroring it to / from GoB.
# direction can be ==> or <=>
REPOSITORIES=(
"https://bazel.googlesource.com/bazel ==> git@github.com:bazelbuild/bazel.git bazel"
- "https://bazel.googlesource.com/bazel-toolchains <=> git@github.com:bazelbuild/bazel-toolchains.git bazel-toolchains"
"https://bazel.googlesource.com/java_tools ==> git@github.com:bazelbuild/java_tools.git java_tools"
"https://bazel.googlesource.com/rules_cc ==> git@github.com:bazelbuild/rules_cc.git rules_cc"
"https://bazel.googlesource.com/tulsi ==> git@github.com:bazelbuild/tulsi.git tulsi"
