Major refactor & optimization of how modules load their packages

Now that we are loading package autoloads files (as part of the
generated doom-package-autoload-file when running make autoloads), many
:commands properties are redundant. In fact, many def-package! blocks
are redundant.

In some cases, we can do without a config.el file entirely, and can move
into the autoloads file or rely entirely on package autoloads.

Also, many settings have been moved in their module's autoloads files,
which makes them available ASAP; their use no longer depends on module
load order.

This gained me a modest ~10% boost in startup speed.

modules/lang/cc/autoload.el

@@ -89,13 +89,6 @@ compilation dbs."
                         nconc (list "-I" path)))
        (doom-project-root)))))
 
-;;;###autoload
-(defun +cc|init-rtags ()
-  "Start an rtags server in c-mode and c++-mode buffers."
-  (when (and (memq major-mode '(c-mode c++-mode))
-             (rtags-executable-find "rtags"))
-    (rtags-start-process-unless-running)))
-
 ;;;###autoload
 (defun +cc|cleanup-rtags ()
   "Kill rtags server(s) if there are no C/C++ buffers open."