chore: remove unused proto imports (#149)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 468735472

Source-Link: googleapis/googleapis@cfa1b37

Source-Link: googleapis/googleapis-gen@09b7666
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiMDliNzY2NjY1NjUxMGY1YjAwYjg5M2YwMDNhMGJhNTc2NmY5ZTI1MCJ9

Author: gcf-owl-bot[bot]

packages/google-api-servicecontrol/protos/google/api/servicecontrol/v1/service_controller.proto

@@ -20,7 +20,6 @@ import "google/api/annotations.proto";
 import "google/api/client.proto";
 import "google/api/servicecontrol/v1/check_error.proto";
 import "google/api/servicecontrol/v1/operation.proto";
-import "google/protobuf/timestamp.proto";
 import "google/rpc/status.proto";
 
 option cc_enable_arenas = true;