Remove "conflicted" as transaction category.

We were losing information about sent/received by overriding the
category in case of a conflicted transaction.

Hence, remove the "conflicted" category.

Conflicted status of a transaction can still be determined by looking
for confirmations<0.
Merge pull request #3720

b96f6a7 Remove "conflicted" as transaction category. (Wladimir J. van der Laan)