[docs] Remove GCC build info

docs/build_linux.md

@@ -40,13 +40,6 @@ Please see instructions [here](https://github.com/Microsoft/AirSim/blob/master/d
    ./build.sh
    ```
 
-  Optionally, if you need GCC binaries for some other reason, you can simply add gcc to the setup and build invocation, like this:
-
-   ```bash
-   ./setup.sh --gcc
-   ./build.sh --gcc
-   ```
-
 ### Build Unreal Environment
 
 Finally, you will need an Unreal project that hosts the environment for your vehicles. AirSim comes with a built-in "Blocks Environment" which you can use, or you can create your own. Please see [setting up Unreal Environment](unreal_proj.md).