Remove deprecated env variable in docs (#2936)

Remove the usage of the REMOTE_DEPLOYMENT environment variable (e.g.,
export REMOTE_DEPLOYMENT=3) from the example code blocks in the
[IsaacLab App
documentation](https://isaac-sim.github.io/IsaacLab/main/source/api/lab/isaaclab.app.html),
as this variable has been deprecated.

Fixes #2920  (issue)

- Bug fix (non-breaking change which fixes an issue)

Before
<img width="817" height="279" alt="isaaclab_app"
src="https://github.com/user-attachments/assets/cfd45532-8b43-4285-9ed9-81039c7624e1"
/>
After
<img width="810" height="256" alt="Screenshot from 2025-07-15 09-54-47"
src="https://github.com/user-attachments/assets/65838873-7374-4eee-8963-f35ca661725e"
/>

- [O] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [O] I have made corresponding changes to the documentation
- [O] My changes generate no new warnings
- [O] I have added tests that prove my fix is effective or that my
feature works
- [X] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [O] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

CONTRIBUTORS.md

@@ -91,6 +91,7 @@ Guidelines for modifications:
 * Michael Gussert
 * Michael Noseworthy
 * Miguel Alonso Jr
+* Mingyu Lee
 * Muhong Guo
 * Nicola Loi
 * Norbert Cygiert