Simplify hooking of contrib keymaps into core keymaps

* contrib/sly-autodoc.el (sly-autodoc-enable): Removed.
(sly-autodoc): Hooks can/should carry the minor
mode's function, no need for an "-enable" helper.

* contrib/sly-stickers.el (sly-stickers): oHooks can/should carry the minor
mode's function, no need for an "-enable" helper.
(sly-stickers-enable, sly-stickers-shortcuts-enable): Deleted.

* contrib/sly-trace-dialog.el (sly-trace-dialog-enable): Removed.
(sly-trace-dialog): Hooks can/should carry the minor
mode's function, no need for an "-enable" helper.