Fix AMBuild for python 3.12

[Kenzzer]

https://docs.python.org/3/whatsnew/3.12.html

• The asynchat, asyncore, and imp modules have been removed, along with several unittest.TestCase method aliases.

https://github.com/alliedmodders/ambuild/blob/417517c1ec86c0a1a90e1ad37faf0b8b68654fa3/ambuild2/context.py#L19

imp is being imported in context.py but not used, let's strip that ?

[dvander]

Thanks!