Use lexical-bindin in Ibuffer.

Use lexical-bindin in Ibuffer.
* lisp/ibuffer.el (ibuffer-do-toggle-read-only): `arg' is unused.
(ibuffer-compile-format): Simplify.
(ibuffer-clear-summary-columns): Simplify.
* lisp/ibuf-ext.el (ibuffer-generate-filter-groups): Don't use the third
elem of dotimes when we don't refer to the iteration var from it.
(ibuffer-toggle-sorting-mode): Avoid add-to-list.
* lisp/ibuf-macs.el (define-ibuffer-column, define-ibuffer-op):
Silence byte-compiler.