Disable unit tests for SDL2 builds.

SDL_KillThread or an equivalent doesn't exist in SDL2. Achieving the same
functionality the "SDL2 way" is problematic here, so I'll just disable this
code for now.
SotBE S7: have scorpions target all side 1 units, not just Kapou'e

The scorpions have no concept of a side leader.  This only affects
moves toward targets, attacks were already done in this way,