Simplify and speed up the kyua build

Instead of having multiple kyua libraries, just include the files as part
of usr.bin/kyua. Previously, we would build each kyua source up to four
times: once as a .o file and once as a .pieo. Additionally, the kyua
libraries might be built again for compat32. As all the kyua libraries
amount to 102 C++ sources the build time is significant (especially when
using an assertions enabled compiler). This change ensures that we build
306 fewer .cpp source files as part of buildworld.

Reviewed By: brooks
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D30967