Set empty security policy

[chrisst]

fixes hashicorp/terraform-provider-google#3948

Release Note for Downstream PRs (will be copied)

Allow security policy to be removed from `google_backend_service`

[rileykarson]

Should we add a test as well? Updating fields to empty values often doesn't work as expected, and that way we'll have historical debug logs if the API behaviour changes on us.

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
This PR seems not to have generated downstream PRs before, as of 2dd8d8b.

Pull request statuses

No diff detected in terraform-google-conversion.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#916
depends: hashicorp/terraform-provider-google#3969

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, 40c14af.

Pull request statuses

terraform-provider-google-beta already has an open PR.
No diff detected in terraform-google-conversion.
terraform-provider-google already has an open PR.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I didn't open any new pull requests because of this PR.