Changes 'unalias' to 'unset' inside setup_conda_env in orbit.sh (#378)

The line `'unalias ORBIT_PATH &>/dev/null'` inside `setup_conda_env()`
prevents `orbit.sh --conda` to successfully exit. The "`unset`" command
rather than "`unalias`" should be used for environment variables (e.g.,
`ORBIT_PATH`). This is a problem, e.g., when a custom dockerfile is used
to directly install conda during the image build process: the image
build process is interrupted.

Fixes #377

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

Before:

https://github.com/NVIDIA-Omniverse/orbit/blob/a642b8e32cf07efa11a583e8db3680d971922e1e/orbit.sh#L148
After:
`'unset ORBIT_PATH' \`

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

CONTRIBUTORS.md

@@ -39,6 +39,7 @@ Guidelines for modifications:
 * Jia Lin Yuan
 * Jingzhou Liu
 * Kourosh Darvish
+* Özhan Özen
 * Qinxi Yu
 * René Zurbrügg
 * Ritvik Singh

orbit.sh

@@ -145,7 +145,7 @@ setup_conda_env() {
     printf '%s\n' '#!/usr/bin/env bash' '' \
         '# for orbit' \
         'unalias orbit &>/dev/null' \
-        'unalias ORBIT_PATH &>/dev/null' \
+        'unset ORBIT_PATH' \
         '' \
         '# for isaac-sim' \
         'unset CARB_APP_PATH' \