Remove ancient CSS (and its counter) to fix <code> alignment

What does this MR do and why?

The table a code in common.scss was added in 5f4a7c3e (16y ago), and then 0aba37cf was added (12y ago) to negate that (!) in diff comments. Rapid diffs render in tables, so the first is applying without the second negating it, causing inline code in links in rapid diffs to appear too high for the baseline.

This also applies to just any code in link in tables in regular comments!

The rule was originally written for tables listing commits, those long since gone, so just removing it (and then removing the override) fixes it everywhere.

Closes Rapid diff comment <code> style somewhat elevated (#622059).

Screenshots or screen recordings

Where	Before	After
Rapid diffs
Tables in any Markdown content

How to set up and validate locally

1. Write a comment like this on a rapid diff:

   [hello `friend` yay](bweh)

2. Note friend is slightly too high for its own good, per the top-left image in the table above.
3. Write a comment like this in any Markdown field elsewhere on the site:

   | hmm | ok |
   | --- | -- |
   | [well `stonks` then](uhm) | wao |

4. The stonks are also uncomfortably perched, per the bottom-left image in the table.
5. Check out this branch and let the CSS changes roll in.
6. Re-verify both cases now reflect the right-hand side of the table, nestled among their word-friends upon the safety of the baseline.

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