Bump libressl's version in pkgconfig to 2.0.0

Bump libressl's version in pkgconfig to 2.0.0

LibreSSL's pc files effectively hardcode the version to 1.0.0 since
LibreSSL exists. That probably never made much sense. This causes
some pain for ports that "need 'openssl' ['>= +1.1.0'] found '1.0.0'"
or similar while they would build perfectly fine with LibreSSL.
This only affects OpenBSD. We do not put the actual LibreSSL version
in there since it may cause trouble

Discussed with sthen, millert, inoguchi, beck over the past year.

Diff from/ok sthen