Remove defunct custom-faces in custom.el

These are now set via use-package's :custom-face option.

custom.el

@@ -12,6 +12,4 @@
  ;; If you edit it by hand, you could mess it up, so be careful.
  ;; Your init file should contain only one such instance.
  ;; If there is more than one, they won't work right.
- '(go-guru-hl-identifier-face ((t (:background "gray30"))))
- '(markdown-code-face ((t nil)))
- '(sp-pair-overlay-face ((t (:inherit nil)))))
+ )