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GH-40074: [C++][FS][Azure] Implement `DeleteFile()` for flat-namespace storage accounts (#40075)

### Rationale for this change

It was not implemented yet.

### What changes are included in this PR?

 - An implementation of `DeleteFile()` that is specialized to storage accounts that don't have HNS support enabled
 - This fixes a semantic issue: deleting a file should not delete the parent directory when the file deleted was the last one
 - Increased test coverage
 - Fix of a bug in the version that deletes files in HNS-enabled accounts (we shouldn't let `DeleteFile` delete directories even if they are empty)

### Are these changes tested?

Yes. Tests were re-written and moved to `TestAzureFileSystemOnAllScenarios`.
* Closes: #40074

Lead-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Co-authored-by: jerry.adair <Jerry.Adair@sas.com>
Signed-off-by: Felipe Oliveira Carvalho <felipekde@gmail.com>