Minor CMake cleanup and KratosMultiphysics install logic.

[roigcarlo]

A couple of changes to the CMakeFile:

• Temporally removing the packaging as it was not working anyway. The aim is to enable it again in the new version
• KratosMultiphysics folder has a custom install script now which deletes the folder on "make install" (not on configure) so changes in the python modules and old applications not compiled should no longer give problems.

This should fix #4296 and... another one, sorry don't remember the number (@philbucher is the one with the problem with the FluidDynamicsApplication from @armingeiser I think ?)

[jcotela]

Should we remove libs/ too? I guess it should not be that much of a problem with the current setup, but we can still be keeping outdated .so files there.

[roigcarlo]

@jcotela Done, but I will try it on win first in the rare case it decides to change the order of the commands for some reason.

[armingeiser]

Yes it was #2848

[philbucher]

works for me, thx a lot @roigcarlo !

[jcotela]

Appveyor passed, looks like it should work in windows too 👍