security/acme-client: Fix runtime when SSL_DEFAULT != libressl

• Make sure we link with libthr as well to prevent runtime errors like "tls_init: No error: 0" [1].

• Adopt the nicer approach for linking with libtls taken by net/openntpd; it doesn't require patching of build files [2].

• Remove unused patch

PR: 228438
Submitted by: madpilot, tobik [1], leres [2]
Reported by: dch
Approved by: brnrd (maintainer timeout, 2 weeks)