Revert "Close handles opened with dlopen()"
This reverts commit 699b03a. This was causing the profiler tooling extension to be unloaded so that running the profiler with eg: rbx -Xprofile -e 'p 1' would cause an EXC_BAD_ACCESS on OS X Maverics at least. Generally, we don't want to dlclose() a library that we loaded and intend to use. We may address this by passing RTDL_NODELETE to dlopen(), but that mode flag is not universally supported and was added later. If we don't intend to unload the library, there's no reason to dlclose() it before process exit.