Remove RUN SCRIPT from KSQL syntax

[big-andy-coates]

Issue #2179 saw the RUN SCRIPT functionality being dropped from the rest API and being replaced by functionality within the CLI to pass the script contents in the request body.

However, RUN SCRIPT remains in the KSQL syntax. This issue is here to track the removal of it from the syntax on the next major version bump.

This will mean users of the RESTful API will receive a parser error should they submit a RUN SCRIPT request, rather than the current message explaining its no longer supported. (Note, the CLI still supports RUN SCRIPT).

To support RUN SCRIPT statements already in the command queue we may chose to add custom handling - or make a breaking change. TBD.