Remove vestigial Versioneer support

[nutjob4life]

💡 Description

An earlier version of the PDS template repository for Python projects included Versioneer as a way to automatically handle package versioning.

This proved to be far too troublesome and error-prone and conflicted with other CI tools, so we dropped it.

However, some vestigial bits of Versioneer support remains in the repository and these should be removed:

• Removal of the .gitattributes file completely
• Deletion of versioneer.py and _version.py in the MANIFEST.in file
• Expunging of _version.py in the [coverage:run] section of setup.cfg
• Abolishment of the [mypy-pds.*._version] section completely from setup.cfg
• Excision of the entire [versioneer] section from setup.cfg