Revert Makefile changes from 2bcfb38c31
The idea from 2bcfb38c31 was to have the main make target, which would
be used in production, have assertions disabled, and the debug target,
which tests are run against, would have them enabled.
However this didn't work out in practice, since during the Debian
package build process, it would run tests through make test, which
rebuilds poolcounterd again, except with debugging enabled, and packages
By reverting those changes, there is only one type of build of
poolcounterd, and that has assertions enabled. And running "make test"
won't rebuild poolcounterd every single time.