Make wsutil depend on gitversion.

wsutil contains the only code that uses version.h; make the dependency
explicit, to see whether that fixes the current build issues with Debian
packaging.

Also, get rid of all *other* dependencies on gitversion.

Change-Id: I89fa5e4112633b83a1a7dfa349bc337e3688575f
Reviewed-on: https://code.wireshark.org/review/2823
Reviewed-by: Guy Harris <guy@alum.mit.edu>