chore: remove unused proto imports (#682)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 468735472

Source-Link: googleapis/googleapis@cfa1b37

Source-Link: https://github.com/googleapis/googleapis-gen/commit/09b7666656510f5b00b893f003a0ba5766f9e250
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiMDliNzY2NjY1NjUxMGY1YjAwYjg5M2YwMDNhMGJhNTc2NmY5ZTI1MCJ9

Author: gcf-owl-bot[bot]

protos/google/cloud/language/v1beta2/language_service.proto

@@ -20,7 +20,6 @@ package google.cloud.language.v1beta2;
 import "google/api/annotations.proto";
 import "google/api/client.proto";
 import "google/api/field_behavior.proto";
-import "google/protobuf/timestamp.proto";
 
 option go_package = "google.golang.org/genproto/googleapis/cloud/language/v1beta2;language";
 option java_multiple_files = true;