Removes command and cleanups cabal-testsuite.
The tests for #3199 #4099 #3436 are removed, but they seem to be
sandbox specific issues.

Removes Sandbox.Types, Sandbox.Index and Sandbox.Timestamp modules.
The Sandbox and Sandbox.PackageEnvironment are still
there as some configuration in v1-commands happens through them
(~/.cabal/config vs ./cabal.config).

BuildExFlags contained only sandbox specific parameter,
so it's removed as well.

Remove sandbox support from cabal-testsuite
Remove sandbox from GlobalFlags and Sandbox unit-tests