wget: fix ssl detection in static libs configuration

When building wget with openssl in static libs configuration, wget
build system fails detect openssl because it doesn't specify LD flags
for private libs used by openssl. This specifically happens when we
pass --with-libssl-prefix to configure which tries to find ssl using
custom flags. If we don't specify --with-libssl-prefix, it relies on
pkg-config files to detect ssl and it's LD flags which helps with static
linking.

This commit removes --with-libssl-prefix conf opts. Since this case is
similar to gnutls, we remove same conf opts for gnutls as well.

wget can be built with either gnutls or openssl crypto libraries, so
separate optional support for both is not required. This commit also
does minor optimization by checking for either gnutls or openssl while
at it.

Fixes:
  http://autobuild.buildroot.net/results/c6a/c6abdff37b86471cf8b0ceffeff5472042923de0/



Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>