VSTool manipulates the SecondLife.sln solution file for the convenience of a
developer subsequently running Visual Studio interactively. But the cost of
having it sometimes break TeamCity automated builds is too high -- especially
since we never expect to run Visual Studio interactively on a TC build host.

Also remove the CMake UNATTENDED variable that controlled it.

Reviewed by Richard

dataserver-is-deprecated
for-fucks-sake-whats-with-these-commit-markers