oc: Add missing `require'

* lisp/oc.el:
* lisp/oc-basic.el: Add some `require' to avoid compile warnings.

lisp/oc-basic.el

@@ -65,7 +65,10 @@
 ;;; Code:
 
 (require 'bibtex)
+(require 'json)
 (require 'oc)
+(require 'org)
+(require 'seq)
 
 (declare-function org-open-at-point "org" (&optional arg))
 

lisp/oc.el

@@ -57,6 +57,7 @@
 
 (require 'org-compat)
 (require 'org-macs)
+(require 'seq)
 
 (declare-function org-at-heading-p "org" (&optional _))
 (declare-function org-collect-keywords "org" (keywords &optional unique directory))