Workaround for Mono recursion bug when loading assemblies.

Some versions of Mono enter a recursive loop if accessing the assembly name or type from within AssemblyLoad. This works around that by specifically checking for mscorlib or System and aborting early.

This approach forces assembly loading. The iOS sim didn't load System.dll without it.
Merge branch 'hotfix/load-assembly-recursion' of https://github.com/spicypixel/monobjc into spicypixel-hotfix/load-assembly-recursion
Remove unused import.