Just stop adding HPKP(Public-Key-Pins) and HSTS(Strict-Transport-Security) headers to the answers, and after the biggest
max-age value of either of these will expire (meaning no client will remember any longer that your site had these enabled), your site will be free of both HPKP and HSTS.
Also keep in mind that if you had
max-age for HPKP bigger than your current certificate remaining lifetime, you will still need to use the backup key for certificate renewal, or the clients still remebering your backup key hash will think that something nasty is happening on the certificate replacement/renewal.
But it's a really weird intention - while the Web is moving to a more secure state, you wish to move in the opposite direction.