Remove use of `imp` for python 3.12+ upgrade

This was done upstream in two places, neither of which really make sense
to cherrypick:

https://chromium-review.googlesource.com/c/chromium/src/+/2098849
https://chromium-review.googlesource.com/c/chromium/src/+/4714859

Bug: 388344853
Test: mma in external/libchrome; treehugger
Change-Id: Ic6d685d790379ddce33715f595e637d97d2a67f7