Refactor Project API to reflect changes upstream

projectile-project-root no longer returns `default-directory` if not in
a project (it returns nil). As such, doom-project-* functions (and their
uses) have been refactored.

+ doom-project-p & doom-project-root are aliases for
  projectile-project-p & projectile-project-root.
+ doom-project-{p,root,name,expand} now has a DIR argument (for
  consistency, since projectile-project-name and
  projectile-project-expand do not).
+ The nocache parameter is no longer necessary, as projectile's caching
  behavior is now more sane.
+ Removed some projectile advice/hacks that are no longer necessary.
+ Updated unit tests

core/autoload/files.el

@@ -88,8 +88,8 @@ MATCH is a string regexp. Only entries that match it will be included."
       (recentf-add-file new-path))
     (recentf-remove-if-non-kept old-path))
   (when (and (bound-and-true-p projectile-mode)
-             (projectile-project-p)
-             (projectile-file-cached-p old-path (doom-project-root 'nocache)))
+             (doom-project-p)
+             (projectile-file-cached-p old-path (doom-project-root)))
     (projectile-purge-file-from-cache old-path))
   (when (bound-and-true-p save-place-mode)
     (save-place-forget-unreadable-files)))
@@ -111,7 +111,7 @@ MATCH is a string regexp. Only entries that match it will be included."
                             (list new-path))))
          (new-path-dir (file-name-directory new-path))
          (project-root (doom-project-root))
-         (short-new-name (if (file-in-directory-p new-path project-root)
+         (short-new-name (if (and project-root (file-in-directory-p new-path project-root))
                              (file-relative-name new-path project-root)
                            (abbreviate-file-name new-path))))
     (unless (file-directory-p new-path-dir)