Remove instance_group_urls

[c2thorn]

Part of hashicorp/terraform-provider-google#7185

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

container: `instance_group_urls` has been removed in favor of `node_pool.instance_group_urls`

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 6 files changed, 6 insertions(+), 49 deletions(-))
Terraform Beta: Diff ( 6 files changed, 6 insertions(+), 49 deletions(-))
TF OiCS: Diff ( 1 file changed, 2 insertions(+), 2 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 6 files changed, 6 insertions(+), 49 deletions(-))
Terraform Beta: Diff ( 11 files changed, 10 insertions(+), 50 deletions(-))
TF OiCS: Diff ( 1 file changed, 2 insertions(+), 2 deletions(-))

[slevenick]

Upgrade guide already exists for this removal: https://github.com/GoogleCloudPlatform/magic-modules/blob/master/mmv1/third_party/terraform/website/docs/guides/version_4_upgrade.html.markdown#instance_group_urls-is-now-removed

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDatasourceGoogleServiceNetworkingPeeredDnsDomain_basic|TestAccCloudbuildWorkerPool_withNetwork|TestAccCloudFunctionsFunction_vpcConnector|TestAccComputeFirewallPolicyRule_update|TestAccComputeInstanceFromMachineImage_basic|TestAccComputeInstanceFromMachineImage_overrideMetadataDotStartupScript|TestAccComputeInstanceFromMachineImage_diffProject|TestAccComputeOrganizationSecurityPolicyAssociation_organizationSecurityPolicyAssociationBasicExample|TestAccComputeOrganizationSecurityPolicy_organizationSecurityPolicyUpdateExample|TestAccComputeOrganizationSecurityPolicyRule_organizationSecurityPolicyRuleUpdateExample|TestAccComputeRegionNetworkEndpointGroup_regionNetworkEndpointGroupAppengineExample|TestAccContainerAnalysisOccurrence_multipleSignatures|TestAccContainerCluster_backend|TestAccContainerCluster_withNodePoolResize|TestAccContainerNodePool_resize|TestAccContainerNodePool_ephemeralStorageConfig|TestAccServiceNetworkingPeeredDNSDomain_basic|TestAccSqlUser_postgresIAM You can view the result here: https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=213635