Drop the `NO_SYSTEM_ENVIRONMENT_PATH` option from our `find_library`
calls.  No other find modules do this.  Also, since commit
v3.3.0-rc1~430^2 (Teach find_(library|file|path) to get prefixes from
PATH, 2015-02-18) we always search the `lib` directory of each prefix
before the `bin` directory and so should prefer the non-`.dll` name.

Issue: #17336