internal: re-enable generation of customsearch (#511)

This should no longer be an issue to generate now that we make sure we only re-generate newer revisions.

Fixes: #471
diff --git a/google-api-go-generator/gen.go b/google-api-go-generator/gen.go
index 96bc906..e331bbe 100644
--- a/google-api-go-generator/gen.go
+++ b/google-api-go-generator/gen.go
@@ -124,8 +124,7 @@
 
 // skipAPIGeneration is a set of APIs to not generate when generating all clients.
 var skipAPIGeneration = map[string]bool{
-	"customsearch:v1": true,
-	"sql:v1beta4":     true,
+	"sql:v1beta4": true,
 }
 
 func main() {