Remove the unused tags property

And fix up androidmk / bpfix to provide warnings about what to do
instead.

Test: m blueprint_tools  (runs the tests, ensures there aren't any tags left)
Change-Id: I1a3ad8600211050420041740207d6957f44463c8

android/module.go

@@ -191,8 +191,6 @@ type nameProperties struct {
 }
 
 type commonProperties struct {
-	Tags []string
-
 	// emit build rules for this module
 	Enabled *bool `android:"arch_variant"`