ipa-modref-tree.c: fix selftest leaks

ipa-modref-tree.c: fix selftest leaks

"make selftest-valgrind" was reporting:

40 bytes in 1 blocks are definitely lost in loss record 25 of 735
   at 0x483AE7D: operator new(unsigned long) (vg_replace_malloc.c:344)
   by 0xFA0CEA: selftest::test_insert_search_collapse() (ipa-modref-tree.c:40)
   by 0xFA2F9B: selftest::ipa_modref_tree_c_tests() (ipa-modref-tree.c:164)
   by 0x256E3AB: selftest::run_tests() (selftest-run-tests.c:93)
   by 0x1366A8B: toplev::run_self_tests() (toplev.c:2385)
   by 0x1366C47: toplev::main(int, char**) (toplev.c:2467)
   by 0x263203F: main (main.c:39)

40 bytes in 1 blocks are definitely lost in loss record 26 of 735
   at 0x483AE7D: operator new(unsigned long) (vg_replace_malloc.c:344)
   by 0xFA264A: selftest::test_merge() (ipa-modref-tree.c:123)
   by 0xFA2FA0: selftest::ipa_modref_tree_c_tests() (ipa-modref-tree.c:165)
   by 0x256E3AB: selftest::run_tests() (selftest-run-tests.c:93)
   by 0x1366A8B: toplev::run_self_tests() (toplev.c:2385)
   by 0x1366C47: toplev::main(int, char**) (toplev.c:2467)
   by 0x263203F: main (main.c:39)

40 bytes in 1 blocks are definitely lost in loss record 27 of 735
   at 0x483AE7D: operator new(unsigned long) (vg_replace_malloc.c:344)
   by 0xFA279E: selftest::test_merge() (ipa-modref-tree.c:130)
   by 0xFA2FA0: selftest::ipa_modref_tree_c_tests() (ipa-modref-tree.c:165)
   by 0x256E3AB: selftest::run_tests() (selftest-run-tests.c:93)
   by 0x1366A8B: toplev::run_self_tests() (toplev.c:2385)
   by 0x1366C47: toplev::main(int, char**) (toplev.c:2467)
   by 0x263203F: main (main.c:39)

With this patch, the output is clean.

gcc/ChangeLog:
	* ipa-modref-tree.c (selftest::test_insert_search_collapse): Fix
	leak.
	(selftest::test_merge): Fix leaks.