Remove deleted WORKSPACE.go-toolchain from srcs.

TESTED: bazel test //src/test/...

--
MOS_MIGRATED_REVID=109481372
diff --git a/tools/build_rules/go/toolchain/BUILD b/tools/build_rules/go/toolchain/BUILD
index 56c94f1..0bab760 100644
--- a/tools/build_rules/go/toolchain/BUILD
+++ b/tools/build_rules/go/toolchain/BUILD
@@ -35,7 +35,6 @@
     srcs = [
         "BUILD",
         "BUILD.go-toolchain",
-        "WORKSPACE.go-toolchain",
     ],
     visibility = [
         "//src:__subpackages__",