collab: Make unsupported for MinGW toolchain (#23518)

Closes #23451

reverts #23117 for MinGW. collab can't be compiled for MinGW because
webrtc itself doesn't support MinGW compilers

Release Notes:

- N/A

docs/src/development/local-collaboration.md

@@ -6,6 +6,8 @@ First, make sure you've installed Zed's backend dependencies for your platform:
 - [Linux](./linux.md#backend-dependencies)
 - [Windows](./windows.md#backend-dependencies)
 
+Note that `collab` can be compiled only with MSVC toolchain on Windows
+
 ## Database setup
 
 Before you can run the `collab` server locally, you'll need to set up a `zed` Postgres database.

docs/src/development/windows.md

@@ -110,6 +110,8 @@ You can see the [build script](https://github.com/msys2/MINGW-packages/blob/mast
 
 > Please, report any issue in [msys2/MINGW-packages/issues](https://github.com/msys2/MINGW-packages/issues?q=is%3Aissue+is%3Aopen+zed) first.
 
+Note that `collab` is not supported for msys2.
+
 ## Troubleshooting
 
 ### Setting `RUSTFLAGS` env var breaks builds