Simplify EMIT-VOP further.

Simplify EMIT-VOP further.

EMIT-VOP is only ever used in conjunction with INSERT-VOP-SEQUENCE, by
returning two values: first and last VOPs, all linked together,
INSERT-VOP-SEQUENCE then inserts them into the block. But nowadays
EMIT-VOP always returns the same VOP as the second value.
* EMIT-VOP now returns one value, the emitted VOP.
* INSERT-VOP-SEQUENCE is renamed to INSERT-VOP, accepts only one VOP.
* A new function EMIT-AND-INSERT-VOP is added, which combines them,
  and is used anywhere where EMIT-VOP was used.

This makes things less complicated, and reduces core size by 32KB, the
same as the previous commit, for a total of 64KB of savings
essentially for free.

(Also squeeze a couple of line-break fixes)