Clean up and improve compilation of arithmetic (bug#42597)

Clean up and improve compilation of arithmetic (bug#42597)

* lisp/emacs-lisp/byte-opt.el (byte-optimize-associative-math)
(byte-optimize-min-max): Transform 3-arg min/max call into two 2-arg
calls, which is faster.
* lisp/emacs-lisp/bytecomp.el (byte-compile-associative): Rename to...
(byte-compile-variadic-numeric): ...this function and simplify,
fixing incorrect comments.  The 3-arg strength reduction is now
always done in the optimisers and is no longer needed here.
(byte-compile-min-max): New function.
(byte-compile-minus): Simplify, remove incorrect comment, and use
byte-compile-variadic-numeric.
(byte-compile-quo): Simplify and fix comment.