gh-100689: Revert "bpo-41798: pyexpat: Allocate the expat_CAPI on the heap memory (GH-24061)" (GH-100745)

* gh-100689: Revert "bpo-41798: pyexpat: Allocate the expat_CAPI on the heap memory (GH-24061)"

This reverts commit 7c83eaa536d2f436ae46211ca48692f576c732f0.
(cherry picked from commit b034fd3e5926c63a681a211087b4c666834c7525)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>