Don't assign the (field t) property to old REPL inputs

Previously, Geiser added a (field t) property to inputs before adding them to the REPL history so it can determine what characters in the buffer belong to old input and yank it when a user pressed enter (geiser-repl--maybe-send) on it. When users recalled an old input with "M-p" (comint-previous-matching-input-from-input), the old input with its (field t) property were inserted after the current prompt. Since old inputs were not "front-sticky," when point was just after the current prompt but before the characters of the old input, Emacs considered point to be outside of the (field t) field; this prevented users from using some movement commands such as forward-word to move point into the old input text. Furthermore, when users inserted text before the old input or yanked other old inputs afterwards, this new text did not have the field property and so Emacs restricted point movement to and from the old text with the (field t) field.

This resolves the issue by not adding the (field t) property to old inputs and instead leverages comint's ability to assign the output field to all non-input (by setting comint-use-prompt-regexp to nil). It should resolve the issue reported in "[Geiser-users] Problem with prompt at history item" by Hamish Ivey-Law (https://lists.nongnu.org/archive/html/geiser-users/2014-12/msg00001.html).