Switch to openssl and install ca-cert bundle

The reason is that the windows schannel code might fail to operate
behind a NTLM proxy.

Switching to openssl also requires to include a CA certificate bundle.
This bundle is generated at compile-time and include in the libcurl-*dll.tar.lzma package
which is by default installed by the mingwGitDevEnv installer.

We also drop the patch which is not required for openssl usage.

See also https://github.com/msysgit/msysgit/commit/3a9151cddd239aab12436ec42b042720c1340f33

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>