Remove the emulate command

[tzraikov]

Users should call tns run ios|android --emulator instead.

[vchimev]

Another option would be to make sure that both commands: tns emulate ios|android and tns run ios|android --emulator do the same think, aliases.

[dtopuzov]

emulate is deprecated in 3.0.0 and will be removed in 3.1.0.