drop empty TARGETS in backends/mediatek/runtime (#21430)

Summary:

The TARGETS file was 0 bytes; BUCK defines the actual neuron_backend
cxx_library targeting Android. fbcode now falls through to BUCK with no
behavior change.

Reviewed By: ndmitchell

Differential Revision: D109082047

Author: bigfootjon

backends/mediatek/runtime/BUCK

@@ -5,11 +5,13 @@ load(
     "@fbsource//tools/build_defs:default_platform_defs.bzl",
     "ANDROID",
 )
+load("@fbcode_macros//build_defs:build_file_migration.bzl", "non_fbcode_target")
 load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "runtime")
 
 oncall("executorch")
 
-runtime.cxx_library(
+non_fbcode_target(
+    _kind = runtime.cxx_library,
     name = "neuron_backend",
     srcs = [
         "NeuronBackend.cpp",