cloud_storage/tests: match topic name when deleting manifest

[abhijat]

when deleting manifest in test_missing_partition we should match topic name with the manifest path. fixes #5711

force push: adjust assertion to happen after topic match

[abhijat]

we were deleting id_allocator manifest sometimes, causing this assertion failure:

[INFO  - 2022-07-28 15:37:48,233 - topic_recovery_test - _find_and_remove_partition_manifest - lineno:392]: manifest f0000000/meta/kafka_internal/id_allocator/0_23/manifest.json is removed, partition-1 last offset is 5032

[Lazin]

LGTM

[abhijat]

there are two failures, not related to this test

#5612 and #5695 which is resolved but this PR did not contain the changes fixing the test

[dotnwat]

rather than doing this, access the name from the topicspec: self.topic is a shortcut if there is exactly one topic, or self.topics[n].name if you have more than one.

[abhijat]

Thanks for the suggestion, I tried this on another PR to sneak in this change there, but it seems this property is only defined for RedpandaTest in rptest.tests.redpanda_test.RedpandaTest.topic whereas this code uses rptest.tests.topic_recovery_test.MissingPartition inherited from rptest.tests.topic_recovery_test.BaseCase neither of which have this property.

It might be good to define a similar property on this test case.