chore(API): Remove unused grouping configs endpoint

[ceorourke]

As far as I can tell this endpoint is not used in favor of ProjectGroupingConfigsEndpoint https://github.com/getsentry/sentry/blob/master/src/sentry/issues/endpoints/project_grouping_configs.py

It isn't published so we don't have to go through the deprecation process, and the front end only uses the project scoped one.

[github-actions]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
30135	2	30133	240

View the top 2 failed test(s) by shortest run time

tests.sentry.hybridcloud.apigateway.test_apigateway.ApiGatewayTest__InMonolithMode::test_region_pinned_urls_are_defined

Stack Traces | 0.467s run time

#x1B[1m#x1B[.../hybridcloud/apigateway/test_apigateway.py#x1B[0m:72: in test_region_pinned_urls_are_defined
    assert (
#x1B[1m#x1B[31mE   AssertionError: REGION_PINNED_URL_NAMES contains sentry-api-0-grouping-configs, but no route is registered with that name#x1B[0m
#x1B[1m#x1B[31mE   assert None#x1B[0m

tests.sentry.hybridcloud.apigateway.test_apigateway.ApiGatewayTest::test_region_pinned_urls_are_defined

Stack Traces | 0.632s run time

#x1B[1m#x1B[.../hybridcloud/apigateway/test_apigateway.py#x1B[0m:72: in test_region_pinned_urls_are_defined
    assert (
#x1B[1m#x1B[31mE   AssertionError: REGION_PINNED_URL_NAMES contains sentry-api-0-grouping-configs, but no route is registered with that name#x1B[0m
#x1B[1m#x1B[31mE   assert None#x1B[0m

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