Revert "streaming: Start to send mutations after PREPARE_DONE_MESSAGE"
Revert "streaming: Start to send mutations after PREPARE_DONE_MESSAGE"

This reverts commit 4c06221766f2005c75e79f5f40713460d5e59252. It breaks
Glauber's upcoming repair series.

scylladb/scylla,raphaelsc/scylla,duarten/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,kjniemi/scylla