doc: remove v14 mention

Author: RafaelGSS

doc/contributing/maintaining/maintaining-openssl.md

@@ -13,8 +13,6 @@ currently need to generate four PRs as follows:
   of this guide.
 * a PR for 16.x following the instructions in the v16.x-staging version
   of this guide.
-* a PR for 14.x following the instructions in the [v14.x-staging version][]
-  of this guide.
 
 ## Use of the quictls/openssl fork