Use a simple C array for the selector types list.
Use a simple C array for the selector types list.

The sparse array is not a particularly good fit.  It allowed us to do a
few things without locking, but those things were not on the critical
path anyway and it added complexity and memory usage for little gain.

This removes the only non-dtable user of the sparse array, which should
mean that we're able to optimise the sparse array for that single use a
bit better.

gnustep/libobjc2,crystax/android-vendor-libobjc2,gnustep/libobjc2,ngrewe/libobjc2,crystax/android-vendor-libobjc2,ngrewe/libobjc2