Make more load-hooks obsolete (Bug#21563)

Make more load-hooks obsolete (Bug#21563)

* lisp/progmodes/dcl-mode.el (dcl-mode):
* lisp/progmodes/idlw-complete-structtag.el: Recommend
with-eval-after-load instead of load-hooks.
* lisp/calc/calc-ext.el (calc-ext-load-hook):
* lisp/emacs-lisp/bytecomp.el (bytecomp-load-hook):
* lisp/emacs-lisp/cl-extra.el (cl-extra-load-hook):
* lisp/emacs-lisp/cl-macs.el (cl-macs-load-hook):
* lisp/emacs-lisp/cl-seq.el (cl-seq-load-hook):
* lisp/gnus/message.el (message-load-hook):
* lisp/gnus/nnheader.el (nnheader-load-hook):
* lisp/gnus/nnmail.el (nnmail-load-hook):
* lisp/progmodes/dcl-mode.el (dcl-mode-load-hook):
* lisp/textmodes/tex-mode.el (tex-mode-load-hook):
* lisp/whitespace.el (whitespace-load-hook): Obsolete for
with-eval-after-load.  Note that these variables are never declared,
but the byte-compiler will still warn about them if used.