Remove proxy tests. Add verify callback tests.

The old proxy tests test the implementation of an application proxy
policy callback defined in the test itself, which is not particularly
useful.

It is, however, useful to test cert verify overrides in
general. Therefore, replace these tests with tests for cert verify
callback behaviour.

Also glob the ssl test inputs on the .in files to catch missing
generated files.

Reviewed-by: Rich Salz <rsalz@openssl.org>