Remove obsolete PDK build functionality

This hasn't worked for a couple years, and continues to bitrot. Just
remove it.

Adds a bpfix rule so that we can eventually remove the
product_variables.pdk definition, which is now always a no-op.

Test: treehugger
Change-Id: I830b54d419b59f6db1d4617b45e61a78234f57a7

cc/rs.go

@@ -26,7 +26,7 @@ import (
 func init() {
 	pctx.VariableFunc("rsCmd", func(ctx android.PackageVarContext) string {
 		if ctx.Config().AlwaysUsePrebuiltSdks() {
-			// Use RenderScript prebuilts for unbundled builds but not PDK builds
+			// Use RenderScript prebuilts for unbundled builds
 			return filepath.Join("prebuilts/sdk/tools", runtime.GOOS, "bin/llvm-rs-cc")
 		} else {
 			return ctx.Config().HostToolPath(ctx, "llvm-rs-cc").String()