gh-109045: Remove remaining LIMITED_API_AVAILABLE checks in tests (#109046)

Commit 13a00078b81776b23b0b6add69b848382240d1f2 (#108663) made all
Python builds compatible with the Limited API, and removed the
LIMITED_API_AVAILABLE flag.  However, some tests were still checking
for that flag, so they were now being incorrectly skipped.  Remove
these checks to let these tests run again.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>