Fix fixnum and unsigned-fixnum array cleanups.

Fix fixnum and unsigned-fixnum array cleanups.

  * dd04bd449535e9016b5652a708a3cac2ca24c87d removes the specialized
array types with specific fixnum widths in favor of more generic
fixnum and unsigned-fixnum array types.

  * In SYS:SRC;CODE;ROOM.LISP, a mistake was made in converting over
to the newer representations, involving an alist of type tag names
to a constant related to the size of array elements.  The mistake
was even made inconsistently, so that neither 32-bit nor 64-bit
targets behaved correctly.

  * Fixed, to use sb!vm:word-shift instead of literal constants.

  * Original report and bisection by akovalenko on #sbcl.