configure: Don't check for malloc hooks that we no longer use.

Commit 825da1c6d1c7 (leak-checker: Remove because it cannot be made
thread-safe.) removed the only uses of these hooks but neglected to remove
the test for them.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Justin Pettit <jpettit@nicira.com>