Revert "Upgrade DCL to v1.21.1"

[slevenick]

Reverts #6576

I believe this causes TestAccClouddeployTarget_Target to fail, not sure why it wasn't present in the original PR though

[modular-magician]

Oops! It looks like no changelog entry is attached to this PR. Please include a release note block in the PR body, as described in https://github.com/GoogleCloudPlatform/magic-modules/blob/master/.ci/RELEASE_NOTES_GUIDE.md:

```release-note:TYPE
Release note
```

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 9 files changed, 13 insertions(+), 226 deletions(-))
Terraform Beta: Diff ( 9 files changed, 13 insertions(+), 226 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2176
Passed tests 1922
Skipped tests: 238
Failed tests: 16

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccFirebaserulesRelease_BasicRelease|TestAccComputeVpnTunnel_defaultTrafficSelectors|TestAccComputeVpnTunnel_vpnTunnelBasicExample|TestAccComputeVpnGateway_targetVpnGatewayBasicExample|TestAccComputeServiceAttachment_serviceAttachmentBasicExampleUpdate|TestAccComputeServiceAttachment_serviceAttachmentExplicitProjectsExample|TestAccComputeInstance_soleTenantNodeAffinities|TestAccComputeForwardingRule_forwardingRuleHttpLbExample|TestAccComputeGlobalForwardingRule_globalForwardingRuleExternalManagedExample|TestAccComputeForwardingRule_forwardingRuleInternallbExample|TestAccComputeForwardingRule_forwardingRuleL3DefaultExample|TestAccComputeForwardingRule_forwardingRuleGlobalInternallbExample|TestAccComputeGlobalForwardingRule_externalHttpLbMigBackendCustomHeaderExample|TestAccComputeForwardingRule_ip|TestAccComputeBackendBucket_externalCdnLbWithBackendBucketExample|TestAccCGCSnippet_eventarcWorkflowsExample

[modular-magician]

Tests passed during RECORDING mode:
TestAccFirebaserulesRelease_BasicRelease[Debug log]
TestAccComputeVpnTunnel_defaultTrafficSelectors[Debug log]
TestAccComputeVpnTunnel_vpnTunnelBasicExample[Debug log]
TestAccComputeVpnGateway_targetVpnGatewayBasicExample[Debug log]
TestAccComputeServiceAttachment_serviceAttachmentBasicExampleUpdate[Debug log]
TestAccComputeServiceAttachment_serviceAttachmentExplicitProjectsExample[Debug log]
TestAccComputeForwardingRule_forwardingRuleHttpLbExample[Debug log]
TestAccComputeGlobalForwardingRule_globalForwardingRuleExternalManagedExample[Debug log]
TestAccComputeForwardingRule_forwardingRuleInternallbExample[Debug log]
TestAccComputeForwardingRule_forwardingRuleL3DefaultExample[Debug log]
TestAccComputeForwardingRule_forwardingRuleGlobalInternallbExample[Debug log]
TestAccComputeGlobalForwardingRule_externalHttpLbMigBackendCustomHeaderExample[Debug log]
TestAccComputeForwardingRule_ip[Debug log]
TestAccComputeBackendBucket_externalCdnLbWithBackendBucketExample[Debug log]

Tests failed during RECORDING mode:
TestAccComputeInstance_soleTenantNodeAffinities[Error message] [Debug log]
TestAccCGCSnippet_eventarcWorkflowsExample[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test