net/libwebsockets: Fix build with LibreSSL

The build system uses both cmake and pkg-config to find OpenSSL and just
combines the results. Our base OpenSSL didn't provide a pkg-config file
until recently, but the LibreSSL port does. From the cmake detection, we
get absolute library paths, from pkg-config just library names (-lssl).
The latter are found in base during linking. The result is linking both
OpenSSL and LibreSSL.

Therefore add a patch that just skips pkg-config for OpenSSL and remove
the broken workaround from the port Makefile.

PR: 271495
Approved by: tcberner (mentor, implicit)