remove unnecessary input

[jdkandersson]

Removes the deprecated base-branch input now that operator-workflows has been updated to no longer use it

[jdkandersson]

I propose we merge this first: https://github.com/canonical/upload-charm-docs/pull/156

[github-actions[bot]]

Test coverage for d2c3f777c107b82bca7bbb8a8e20fb36268be082

Name                      Stmts   Miss Branch BrPart  Cover   Missing
---------------------------------------------------------------------
src/__init__.py              54      0     10      0   100%
src/action.py               156      0     46      0   100%
src/check.py                 29      0     10      0   100%
src/constants.py              4      0      0      0   100%
src/content.py               52      0      8      0   100%
src/discourse.py            156      0     34      0   100%
src/docs_directory.py        29      0      8      0   100%
src/exceptions.py            14      0      0      0   100%
src/index.py                 28      0      6      0   100%
src/metadata.py              28      0     12      0   100%
src/migration.py            106      0     35      0   100%
src/navigation_table.py      53      0     16      0   100%
src/pull_request.py          17      0      4      0   100%
src/reconcile.py             84      0     40      0   100%
src/repository.py           110      0     24      0   100%
src/types_.py               131      0     22      0   100%
---------------------------------------------------------------------
TOTAL                      1051      0    275      0   100%

Static code analysis report

Run started:2023-04-14 08:24:52.385338

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 9690
    Total lines skipped (#nosec): 14
    Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
    Total issues (by severity):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
    Total issues (by confidence):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
Files skipped (0):