comms/wsjtx: prepare for cmake-3.18.x

• this belongs into the "let's forget this ever happened category".
• with cmake-3.18 the target to patch the thirdparty sources gets ran twice. Onde during build and once during the install phase.
• we silently remove the patches again after the build is done, so that during the install phase, the patching is a no-op.

PR: 248003