[CLI] remove js_unittest from casp (#5058)

This PR removes the `js_unittest` command and its associated
implementation from `casp`.

### Reasoning
The `js_unittest` command is deprecated and relies on significantly
outdated versions of Chrome and Chromedriver. As noted in [this
issue](#2678), the current
implementation is unstable/broken. [This
PR](#2689) commented out the
call to this command a while ago.

Fixing this functionality would require a complex migration to the new
Chrome/Chromedriver versioning system, which is described
[here](https://developer.chrome.com/docs/chromedriver/downloads/version-selection).
Since the command is already deprecated, we have decided to remove it
rather than investing resources in the upgrade for now.

### Changes
Removed the `js_unittest` source file.

Removed the command registration and module calls in the main script.

Author: PauloVLB

cli/casp/src/casp/commands/js_unittest.py

@@ -21,7 +21,6 @@
 from casp.commands import hi
 from casp.commands import init
 from casp.commands import integration_tests
-from casp.commands import js_unittest
 from casp.commands import lint
 from casp.commands import package
 from casp.commands import py_unittest
@@ -48,7 +47,6 @@ def cli():
 cli.add_command(reproduce.cli)
 cli.add_command(bootstrap.cli)
 cli.add_command(py_unittest.cli)
-cli.add_command(js_unittest.cli)
 cli.add_command(format_command.cli)
 cli.add_command(lint.cli)
 cli.add_command(package.cli)