Fix: Edited messages appear twice in fulltext search

[adnull]

As stated in https://github.com/matrix-org/dendrite/issues/3358 the search response contains both original and edited message. This PR fixes it by removing of the original message from the fulltext index after indexing the edit message event. I also made some cosmetic changes/fixes i found in the code

Signed-off-by: Alexander Dubovikov <[email protected]>