configure: remove useless -Wno-* from default CFLAGS

configure: remove useless -Wno-* from default CFLAGS

Historically we always had -Wno-unused-parameter and
-Wno-unused-function enabled along with -Wall.

When we made -Wall a default option, we carried the other two along and
made them default too (in 2018).

Now the code is much cleaner compared to the past and we do not really
require -Wno-unused-parameter and -Wno-unused-function anymore.

Actually they may hide really unused functions that we'd need to
cleanup.

For this reason remove -Wno-unused-parameter and -Wno-unused-function
for good from the default CFLAGS.

Any new warning should rather be fixed than hidden.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20211005122736.4060-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22917.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 01ce6ca39d1f4bf45dcd49baede0094c4c990d3b)