Remove legacy admin template files

[phillxnet]

By way of preperation for our next Stable rpm release, it is proposed that we do a little house-keeping regarding some old legacy files, such as those dating back to pre rockstor-jslibs times. An example in this case would be the long defunct Django admin override files found in:

• src/rockstor/templates/admin

Removing their interference with the now way-newer .venv files from our current Django:

• .venv/lib/python3.11/site-packages/django/contrib/admin

[phillxnet]

N.B. we now have a spin-off issue regarding the last, no deleted, comment in this issue:

• File repo relocation clean-ups File repo relocation clean-ups #2944

This is intended to maintain focus on the original issue text: that of the admin files. And to enabled the postponement of the larger concern regarding parntered rockstor-jslibs changes. I.e. we should now leave these larger changes to the next testing phase. Comment to be remarked out accordingly.