fix crash loop on missing manifest tables

[RJKeevil]

Please see https://discuss.hypermode.com/t/manifest-removes-non-existing-table/19882

W are experiencing an error where dgraph tries to remove a table that is missing. I assume that given it has already been removed, it should not trigger a crash loop in compaction. Instead i sense check that the table is indeed removed from all levels, and return without an error code. Please advise if you think this is safe or not.

Checklist

• Code compiles correctly and linting passes locally

[RJKeevil]

@mangalaman93 the test error seems related to the use of t.Cleanup, can you advise?

[mangalaman93]

@mangalaman93 the test error seems related to the use of t.Cleanup, can you advise?

        defer removeDir(dir)
	deletionsThreshold := 10
	mf, m, err := helpOpenOrCreateManifestFile(dir, false, 0, deletionsThreshold)

	db, err := Open(DefaultOptions(dir))
	require.NoError(t, err, "error while opening db")

	t.Cleanup(func() {
		require.NoError(t, db.Close())
	})

it seems that defer cleaned up the directory and db.Close is not happy about it. I think we should use either t.Cleanup everywhere in this test or defer.

[RJKeevil]

I went back to defer for now to have control over their order, lets see if the tests now pass

[RJKeevil]

and again, with the remove explicitly in the same defer as close db (since they are coupled anyway)

[mangalaman93]

Thank you for the PR @RJKeevil

[RJKeevil]

Thanks for the help @mangalaman93 !