Replace @local_config_platform with @platforms//host

The `local_config_platform` repo is no longer available with Bazel@HEAD.

Author: fmeum

go/private/rules/go_bin_for_host.bzl

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")
+load("@platforms//host:constraints.bzl", "HOST_CONSTRAINTS")
 load("//go/private:common.bzl", "GO_TOOLCHAIN")
 
 def _ensure_target_cfg(ctx):