Update Compilation and Advice chapters in Lisp manual.

Update Compilation and Advice chapters in Lisp manual.

* doc/lispref/advice.texi (Defining Advice): Clarify ad-unadvise.
(Activation of Advice): Specifying the ACTIVATE flag in defadvice
is not abnormal.
(Advising Primitives): Node deleted; ad-define-subr-args has been
removed.

* doc/lispref/compile.texi (Speed of Byte-Code): Use float-time in example.
(Compilation Functions): Note that the log uses Compilation mode.
Don't discuss the contents of byte-code function object here.
(Compilation Functions): De-document internal function byte-code.
(Docs and Compilation): Minor clarifications.

* doc/lispref/objects.texi (Byte-Code Type): Add xref to Byte-Code Function
Objects.

* lisp/emacs-lisp/advice.el: Update commentary to reflect deletion of
ad-define-subr-args