intprops, stdckdint-h: Remove support for IRIX. * lib/intprops-internal.h (_GL_INT_NEGATE_CONVERT): Remove macro. (_GL_EXPR_SIGNED, _GL_INT_MAXIMUM): Use _GL_INT_CONVERT instead. * lib/intprops.h (_GL_DIVIDE_OVERFLOW, _GL_REMAINDER_OVERFLOW): Likewise.