Revert "Adds mViewport to guiTSControl in order to restrict render viewport to a sub-region of the control. This is particularly useful when using a guiTSControl as a container control, as it can restrict the render area to prevent overdraw or dedicate screen space to a panel"

This reverts commit 0c307265a92753eeab4c36bb1d0b4b30976e1d9b.