`sqlx` requires linking against OpenSSL twice:
- `sqlx-macros` needs to link against OpenSSL as a shared libary for use
at compile time.
- `sqlx` needs to link against OpenSSL a static library for use at
runtime.
You can find the details here:
https://github.com/launchbadge/sqlx/issues/670https://github.com/sfackler/rust-openssl/issues/1337
We go with the fix proposed by @sfackler, and add a test program that we
can use to verify everything works correctly.
We remove a few `OPENSSL`-related variables that were added 4 years ago,
and that no longer appear to be needed.
