Removed dolt from the build system

Is ``dolt`` still useful within the mono build system? It seems that some of dolt's caching functionality was incorporated into autotools / libtoolize several years ago, so it may not make as much of a difference to compile times now as it used to. (Source: http://dolt.freedesktop.org/)

I removed the ``dolt`` macros from the build system, then ran ``autogen.sh`` as usual and didn't notice any slowdown in the configuration phase; in fact, it seemed to run slightly faster, though that could just be confirmation bias. The reasoning for using ``dolt`` is to reduce compile times, but now that multicore CPUs are ubiquitous, it seems better to leave it out and run ``make`` in parallel mode, e.g., ``./autogen.sh;make -j4``.