Drop schemaPath function

[P0lip]

schemaPath function relies on Spectral's internals and is used only by AsyncAPI ruleset.

• Remove the SchemaPath usage in AsyncAPI ruleset.
• Create a custom function if we cannot use any other spectral function to achieve the same outcome.
• Use the custom function in the AsyncAPI ruleset.

[philsturgeon]

This is legacy left over from the old example validation code. It should be removed and asyncapi updated to not need it.