deprecate buildtest schema command

[shahzebsiddiqui]

The buildtest schema command is command line interface that comes with ability to display list of schemas, show JSON schema and show example buildspecs for each schema.

Shown below is the example usage

(buildtest) ☁  buildtest [fix_bash_completion_warnings_by_shellcheck] ⚡  buildtest schema -h    
  warnings.warn(
usage: buildtest [options] [COMMANDS] schema [-h] [-e] [-j] [-n Schema Name]

optional arguments:
  -h, --help            show this help message and exit
  -e, --example         Show schema examples
  -j, --json            Display json schema file
  -n Schema Name, --name Schema Name
                        show schema by name (e.g., script)

This is documented https://buildtest.readthedocs.io/en/devel/schema_examples.html with example outputs.

Proposal & Rationale

We can remove this feature from command line since it does not add any value. I doubt anyone would want to view the JSON schema on the command line, and would only need it for development. The examples may be useful but I dont think this adds any value to user.

For instance if one wants to see all example buildspecs for script schema they can run buildtest schema -e -n script.schema.json

The output will show all buildspecs that are valid and invalid. These are used for schema validation and examples are stored in https://github.com/buildtesters/buildtest/tree/devel/buildtest/schemas/examples