Remove constant pool handling logic.

From issue #63:

  This is an artifact of using the ARM code as a base. The ARM
  processor has the ability to do PC relative indexing cheaply and
  thus uses this to reach for 32bit constants.

  On PPC we've elected to follow the model that MIPS uses and load
  32bit constants using 2 instructions. This in theory should
  eliminate the need for the constant pool.

  We not only need to remove the emit of the unused constant pool, but
  all tracking of the constant pool etc.