[5.1/mi] Delete unimplemented ``query'' callback

[Andrew Cagney <ac131313 at cygnus dot com>]

Hello,

The MI documentation currently refers to:

  In addition, the following are still being developed:

  `QUERY'
     This action is currently undefined.

I'd like to delete this comment.

I'll also try to find time to add a comment pointing out that CLI
operations that end up calling query() are not and should not be
supported.


Rationale:

The current CLI in combination with core-gdb can call the function
query() part way through a CLI commands execution.  For instance, during
an expression evaluation, query() can be called to prompt the user for
which, of a number of possible C++ functions, a given function really
is.

This leads to the call stack:

	event loop
	-> cli
	-> core-gdb
	-> query()
	-> read - i.e. event loop

It was thought that the ``QUERY'' action was a possible way of making it
possible for the MI to provide access to the CLI.  An MI interaction
largely mimic the above - the query would be a call-back.

My understanding is that core-gdb and the CLI are currently trying to
untangle themselves (the GDB interface) and in doing so will eliminate
any need for a query() function.  MI's QUERY call-back would make this
work difficult.

>From conversations, I believe that the current thinking is that MI
operations should be largely self contained - they should not involve
things like call-backs.

Comments?

	Andrew