Delete RenderEngine unused code

* V0 skia implementation beat the prior change deleting unused code, so
delete bindExternalTextureBuffer there.
* Remove useNativeFenceSync, now that there's no more usages
* Remove impl::RenderEngine, since there's no need for a private
impl-superclass spanning every RenderEngine implementation
* Clean up mock/RenderEngine

Bug: 168553972
Test: builds
Change-Id: I6f760510656b90b30d86b04fc70c19067a4491cd
diff --git a/libs/renderengine/skia/SkiaGLRenderEngine.cpp b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
index 94ba153..7cfe207 100644
--- a/libs/renderengine/skia/SkiaGLRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
@@ -193,7 +193,7 @@
 
     // initialize the renderer while GL is current
     std::unique_ptr<SkiaGLRenderEngine> engine =
-            std::make_unique<SkiaGLRenderEngine>(args, display, config, ctxt, placeholder,
+            std::make_unique<SkiaGLRenderEngine>(display, config, ctxt, placeholder,
                                                  protectedContext, protectedPlaceholder);
 
     ALOGI("OpenGL ES informations:");
@@ -246,11 +246,10 @@
     return config;
 }
 
-SkiaGLRenderEngine::SkiaGLRenderEngine(const RenderEngineCreationArgs& args, EGLDisplay display,
-                                       EGLConfig config, EGLContext ctxt, EGLSurface placeholder,
-                                       EGLContext protectedContext, EGLSurface protectedPlaceholder)
-      : renderengine::skia::SkiaRenderEngine(args),
-        mEGLDisplay(display),
+SkiaGLRenderEngine::SkiaGLRenderEngine(EGLDisplay display, EGLConfig config, EGLContext ctxt,
+                                       EGLSurface placeholder, EGLContext protectedContext,
+                                       EGLSurface protectedPlaceholder)
+      : mEGLDisplay(display),
         mEGLConfig(config),
         mEGLContext(ctxt),
         mPlaceholderSurface(placeholder),