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

android/variable.go

@@ -233,7 +233,6 @@ type productVariables struct {
 	Eng                          *bool `json:",omitempty"`
 	Treble_linker_namespaces     *bool `json:",omitempty"`
 	Enforce_vintf_manifest       *bool `json:",omitempty"`
-	Pdk                          *bool `json:",omitempty"`
 	Uml                          *bool `json:",omitempty"`
 	Use_lmkd_stats_log           *bool `json:",omitempty"`
 	Arc                          *bool `json:",omitempty"`