Delete com.facebook.react.modules.debug.NativeSourceCodeSpec

Summary:
When SourceCode was converted to a TurboModule in D17586276, we had to check in `NativeSourceCodeSpec` into the codebase. Since all the OSS NativeModule base classes are now checked into `react-native-github`, it's no longer necessary to keep `NativeSourceCodeSpec`. So, I'm deleting it.

Changelog:
[Android][Removed] - Delete com.facebook.react.modules.debug.NativeSourceCodeSpec

Reviewed By: PeteTheHeat, mdvacca

Differential Revision: D18732997

fbshipit-source-id: 6026b4bcb9ebb9c4d7ba556bc644698eb550a9de

ReactAndroid/src/main/java/com/facebook/react/modules/debug/BUCK

@@ -21,6 +21,9 @@ rn_android_library(
         react_native_target("java/com/facebook/react/turbomodule/core/interfaces:interfaces"),
         react_native_target("java/com/facebook/react/uimanager:uimanager"),
     ],
+    exported_deps = [
+        react_native_target("java/com/facebook/fbreact/specs:FBReactNativeSpec"),
+    ],
 )
 
 rn_android_library(

ReactAndroid/src/main/java/com/facebook/react/modules/debug/SourceCodeModule.java

@@ -7,6 +7,7 @@
 
 package com.facebook.react.modules.debug;
 
+import com.facebook.fbreact.specs.NativeSourceCodeSpec;
 import com.facebook.infer.annotation.Assertions;
 import com.facebook.react.bridge.ReactApplicationContext;
 import com.facebook.react.module.annotations.ReactModule;