Remove the unused TypoCorrectionConsumer::MaxEditDistance.

MaxEditDistance was effectively unused as it being initialized to the max
unsigned valued but never updated. Removing it avoids conversion
headaches once the "edit distance" of a typo correction is a weighted
composite of several values instead of roughly the number of characters
changed; comparing the weighted composite value to the number of
characters in a typo would require some form of normalization to make it
comparable to the old, character-based notion of edit distance.

llvm-svn: 149953