feature flag jemalloc should disable/enable all references to jemalloc in source

[sn-suhailm]

When the profiler is run against one of our tests (which doesn't use jemalloc), one of the threads segfaults during thread exit. The stacktrace pointed to doing some jemalloc cleanup which isn't necessary.

A custom build with all the jemalloc code removed worked but ideally the feature flag should be doing this.