Remove extraneous compile of non existent file.

Merge to v6.0
* Parameterized comment-reader over 'unsyntax, for use with RACKETBLOCK
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
* Updated manual to explain #:escape-id parameter to comment-reader
  pkgs/scribble-pkgs/scribble-doc/scribblings/scribble/manual.scrbl
* Changed parameter name to #:escape-id.
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
* Changed parsing for #:escape-id to use a peeking-input-port.
  pkgs/scribble-pkgs/scribble-lib/scribble/comment-reader.rkt
scribble/comment-reader doc tweaks