Use the gsutil rm command:
gsutil rm gs://[BUCKET_NAME]/[OBJECT_NAME]
[BUCKET_NAME] is the name of the bucket containing the object you want to delete. For example, my-bucket.
[OBJECT_NAME] is the name of the object you want to delete. For example, pets/dog.png.
If successful, the response looks like the following example:
Operation completed over 1 objects.