chore: remove unused imports (#391)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 439804516

Source-Link: googleapis/googleapis@ef938a4

Source-Link: googleapis/googleapis-gen@0f1febd
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiMGYxZmViZDFlMDRkNjhmN2Y1MjQwN2EzMmFkMzgyNjlhMGMwZWE0YiJ9

Author: gcf-owl-bot[bot]

packages/google-devtools-containeranalysis/protos/google/devtools/containeranalysis/v1/containeranalysis.proto

@@ -22,9 +22,6 @@ import "google/api/field_behavior.proto";
 import "google/api/resource.proto";
 import "google/iam/v1/iam_policy.proto";
 import "google/iam/v1/policy.proto";
-import "google/protobuf/timestamp.proto";
-import "grafeas/v1/common.proto";
-import "grafeas/v1/grafeas.proto";
 import "grafeas/v1/severity.proto";
 
 option csharp_namespace = "Google.Cloud.DevTools.ContainerAnalysis.V1";