Remove EOL Python 2 rosdep keys

[mjcarroll]

Based on this: #51650

@cottsay proposed that we remove all existing python2 keys from rosdistro, as Python 2.7 is long EOL.
We should do this in batches of approximate 20% of the keys from lowest risk to highest risk of anybody depending on them (though they really, really shouldn't at this point).

Batches Checklist:

• Stage 1 (20%): rosdep: drop legacy Python 2 keys - Stage 1 (20%) #51716
• Stage 2 (40%): rosdep: drop legacy Python 2 keys - Stage 2 (40%) #51717
• Stage 3 (60%): rosdep: drop legacy Python 2 keys - Stage 3 (60%) #51718
• Stage 4 (80%): rosdep: drop legacy Python 2 keys - Stage 4 (80%) #51719
• Stage 5 (100%): rosdep: drop legacy Python 2 keys - Stage 5 (100%) #51720