Revert unnecesary lcase in ds-identify

[akutz]

Proposed Commit Message

Revert unnecesary lcase in ds-identify

This patch reverts an unnecessary lcase optimization in the
ds-identify script. SystemD documents the values produced by
the systemd-detect-virt command are lower case, and the mapping
table used by the FreeBSD check is also lower-case.

The optimization added two new forked processes, needlessly
causing overhead.

Additional Context

Please see #970 (comment) for more information.

cc @smoser

Test Steps

$ make clean_pyc && PYTHONPATH="$(pwd)" python3 -m pytest -v tests/unittests/test_ds_identify.py

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly