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

modules/feature/eval/autoload/repl.el

@@ -11,7 +11,7 @@
              (unless (buffer-live-p buffer)
                (remhash key +eval-repl-buffers)))
            +eval-repl-buffers)
-  (let* ((project-root (doom-project-root 'nocache))
+  (let* ((project-root (doom-project-root))
          (key (cons major-mode project-root))
          (buffer (gethash key +eval-repl-buffers)))
     (cl-check-type buffer (or buffer null))