taglibextractor: Restore extracting audio props without tags existing

Summary:
7f9de32eedff7f81818145001fc38bbed01de1b7 made extraction of audio
properties depending on the presence of any tag, by moving the extraction
into the "if (!tags->isEmpty())" branch.
This dependency is not necessary and prevents extracting the audio data
for files without a tag (as sideeffect broke a test in baloo-widgets).

Existing sample autotest files in no-meta/ subdir have not catched this,
as they still had an ID3 tag content (TSSE), so tags->isEmpty() was false.

Patch removes all metadata from the existing no-meta files, and fixes the resulting test failures

Test Plan:
Tests wit the updated no-meta test files do no longer fail
Unit test extractortest in baloo-widgets also works again, as audio metadata
is extracted again from a file with no id3 data.

Reviewers: mgallien, michaelh, kossebau

Reviewed By: mgallien

Subscribers: kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D13885