leveldb: do not link tcmalloc

tcmalloc comes in google-perftools.  Programs dynamically linking
the leveldb library will segfault during link because of tcmalloc.
Make check does not pass if google-perftools is installed first.

This patch removes the test for tcmalloc and uses the default system
malloc instead.

Closes #17892.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>