peer: properly clean up chanMsgStreams map on readHandler exit
peer: properly clean up chanMsgStreams map on readHandler exit

This commit ensures that all references within the chanMsgStreams are
all removed and deleted when the readHandler exits. This ensures that
all objects don’t have extra references, and will properly be garbage
collected.

aakselrod/lnd,LightningNetwork/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,aakselrod/lnd