Issue #19493: Refactor ctypes test package.

Issue #19493: Refactor ctypes test package.

Skipped tests are now marked as skipped, formerly commented-out or
renamed-so-it-doesn't-look-like-a-test tests are uncommented, properly named,
and unconditionally skipped, some tests that simply didn't run before
are now able to run, and a few are split into multiple methods instead of
skipping via 'return' in the middle of a method.  Also, a couple of unused
files are removed completely.