chore: removed some unused vars (#4175)

Removed some unused vars pointed by
https://github.com/cameron-martin/bazel-lsp (on not yet merged version).

**What type of PR is this?**
Cleanup

go/private/rules/cross.bzl

@@ -52,7 +52,6 @@ def _go_cross_impl(ctx):
     old_default_info = ctx.attr.target[DefaultInfo]
     old_executable = old_default_info.files_to_run.executable
 
-    new_default_info = None
     if old_executable:
         # Bazel requires executable rules to created the executable themselves,
         # so we create a symlink in this rule so that it appears this rule created its executable.

go/private/rules/test.bzl

@@ -656,7 +656,6 @@ def _recompile_external_deps(go, external_source, internal_archive, library_labe
     i = 0
     for label in dep_list:
         i += 1
-        recompile_suffix = ".recompile%d" % i
 
         # If this library is the internal archive, use the recompiled version.
         if label == internal_archive.data.label:

go/private/rules/transition.bzl

@@ -87,9 +87,7 @@ def _go_transition_impl(settings, attr):
         pure = "off"
         settings["//go/config:pure"] = False
     if pure == "on":
-        race = "off"
         settings["//go/config:race"] = False
-        msan = "off"
         settings["//go/config:msan"] = False
     cgo = pure == "off"
 

go/private/sdk.bzl

@@ -546,7 +546,6 @@ def detect_host_platform(ctx):
     return goos, goarch
 
 def _detect_host_sdk(ctx):
-    root = "@invalid@"
     if "GOROOT" in ctx.os.environ:
         return ctx.os.environ["GOROOT"]
     res = ctx.execute([executable_path(ctx, "go"), "env", "GOROOT"])

proto/def.bzl

@@ -43,8 +43,6 @@ load(
 GoProtoImports = provider()
 
 def get_imports(attr, importpath):
-    proto_deps = []
-
     # ctx.attr.proto is a one-element array since there is a Starlark transition attached to it.
     if hasattr(attr, "proto") and attr.proto and types.is_list(attr.proto) and ProtoInfo in attr.proto[0]:
         proto_deps = [attr.proto[0]]

tests/core/go_proto_library_importpath/BUILD.bazel

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+load("@io_bazel_rules_go//go:def.bzl", "go_test")
 load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
 load("@rules_proto//proto:defs.bzl", "proto_library")