CMake: Avoid unnecessary link dependency with SBC and fix debian warnings

CMake: Avoid unnecessary link dependency with SBC and fix debian warnings

Fixes dpkg warnings:

  dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/wireshark-qt/usr/bin/wireshark was not linked against libsbc.so.1 (it uses none of the library's symbols)
  dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/wireshark-gtk/usr/bin/wireshark-gtk was not linked against libsbc.so.1 (it uses none of the library's symbols)
  dpkg-shlibdeps: warning: symbol sbc_decode used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries
  dpkg-shlibdeps: warning: symbol sbc_init used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries
  dpkg-shlibdeps: warning: symbol sin used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries
  dpkg-shlibdeps: warning: symbol floorf used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries
  dpkg-shlibdeps: warning: symbol floor used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries
  dpkg-shlibdeps: warning: symbol sbc_finish used by debian/libwscodecs0/usr/lib/x86_64-linux-gnu/libwscodecs.so.0.0.0 found in none of the libraries

Change-Id: I71911513c348edd336cdc82ea358b6a05760b4b9
Reviewed-on: https://code.wireshark.org/review/13784
Petri-Dish: João Valverde <j@v6e.pt>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Balint Reczey <balint@balintreczey.hu>