This commit removes the default prompt value from the `spell-replace`
command.
Currently, running the command after selecting a misspelled word
might not allow the editor to propose alternative spellings because
it completes upon whatever is inserted into the prompt. If the words
returned by `aspell` are too different from the currently misspelled
word, no candidates are shown.
For example, selecting “unanymously” and running `:spell-replace`
will not show any candidates under the current implementation (the
‘y’ probably trips the fuzzy-matcher).
The user develops a habit of clearing the prompt every time, because
that's the only way to make sure all suggestions from `aspell` are
visible, so the editor might as well not have any default value for
`:spell-replace`.
efb6fca068