configure: Remove WinCrypt checks

Stop testing for WinCrypt functions, since the code itself does not
contain support anymore. This fixes --without-cng builds which still try
to fall back to WinCrypt.

Sync with cmake, i.e. claim support as soon as bcrypt.h is found.

Resolves #3460

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>