Remove a comment asking a question, as the answer is "no".

I.e., no, the epan/decode_as.c stuff belongs in libwireshark, not libui,
because dissectors need to be able to say "I support decode-as...".
Code to implement the UIs that allow decode-as entries to be specified
would belong in libui.

Change-Id: Ibf9da19e752481a3892d0f03d0a0537590ab1811
Reviewed-on: https://code.wireshark.org/review/3416
Reviewed-by: Guy Harris <guy@alum.mit.edu>