Move `with_testrepos` to `deprecated`?

[mih]

#6690 removes the last traces of its usage from the core package.

From my POV there are only few points of usage left across all extensions, and all in deprecated

./deprecated/datalad_deprecated/tests/test_auto.py:@with_testrepos('basic_annex', flavors=['clone'])
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])  #TODO: Use all repos after fixing them
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('basic_git', flavors=['local'])
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])  #TODO: Use all repos after fixing them
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])
./deprecated/datalad_deprecated/tests/test_publish.py:@with_testrepos('submodule_annex', flavors=['local'])  #TODO: Use all repos after fixing them
./deprecated/build/lib/datalad_deprecated/tests/test_auto.py:@with_testrepos('basic_annex', flavors=['clone'])

We can either move with_testrepos into this extension and adjust the imports, or change those tests. In either case with_testrepos can be removed from the core package.

[adswa]

Fixed with #7176