Remove rest after implode drum track

I'm new to using MuseScore. I created some music in another software package (LMMS), exported the tracks as MIDI file and loading them in MuseScore so I can print out sheet music.

My problem arises from the drum tracks. The midi file contains the drum instruments as separate instruments (piano) instead of one "drumset". I've successfully loaded four of the instruments and changed them from piano to their respective sounds, which gives me 4 staves, one for each drum instrument.

I'm now merging the 4 staves into one by selecting all staves (ctrl+A) and imploding. The result is is overall good but I noticed that the rests of the bars have been copied into the first bar, even though there is no real rest there anymore.

I've added a before and after example. Note the after example, the top (merged) stave, at the bottom contains the half and quarter rest notes (they are blended in with the bass drum notes).

So my question is, how can I get rid of these rests that are no longer rests? (preferably automatically and not deleting them all one by one)