posix: Fix bug-regex33 after regex sync

On some platforms the inclusion of regex-internal.h in bug-regex33
testcase show a MAX redefinition if test-skeleton.c is include later.
This patch fixes by removing regex-internal.h inclusion and using
SBC_MAX value directly.

Checked on aarch64-linux-gnu.

	* posix/bug-regex33.c: Fix build after regex sync.