This warning is much more appropriate for the compiler, since lexical
binding affects what it can reason and warn about, than for checkdoc
as the warning has no bearing to documentation at all.
The move also improves the reach of the warning.
* etc/NEWS: Update.
* lisp/emacs-lisp/checkdoc.el (checkdoc-lexical-binding-flag)
(checkdoc-file-comments-engine): Move warning from here....
* lisp/emacs-lisp/bytecomp.el (byte-compile-file): ...to here.
* test/lisp/emacs-lisp/bytecomp-resources/no-byte-compile.el:
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-tests--unescaped-char-literals)
(bytecomp-tests-function-put, bytecomp-tests--not-writable-directory)
(bytecomp-tests--target-file-no-directory):
Update tests.
(bytecomp-tests--log-from-compilation)
(bytecomp-tests--lexical-binding-cookie): New test.
* lisp/emacs-lisp/bytecomp.el (byte-compile-file): Document behavior
if 'no-byte-compile' is set.
* test/lisp/emacs-lisp/bytecomp-tests.el
(byte-compile-file/no-byte-compile): New unit test.
* test/lisp/emacs-lisp/bytecomp-resources/no-byte-compile.el: New test
file.
