Fix memory leaks in FFI tests
Fix memory leaks in FFI tests

Some tests only deallocated in the branch where some other test
on the object succeeded.

The ECDH FFI test didn't deallocate any of its objects, which was
missed by valgrind before now because the test was not being run.

Found by Coverity scanner

webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,randombit/botan,webmaster128/botan,randombit/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan