Add GenerateAndroidBuildActions to DefaultsModuleBase

Add an empty GenerateAndroidBuildActiosn to DefaultsModuleBase
so that every defaults module doesn't need to provide one.  This
will also allow adding an implementation in the next patch.

Test: m checkbuild
Change-Id: I13554bdb3a287c2f18e1efab74d4f08a1ba8620c

java/droiddoc.go

@@ -1808,9 +1808,6 @@ type DocDefaults struct {
 	android.DefaultsModuleBase
 }
 
-func (*DocDefaults) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-}
-
 func DocDefaultsFactory() android.Module {
 	module := &DocDefaults{}