...to avoid name collisions and confusion
```
-BEGIN VERIFY SCRIPT-
FILE_LIST=$(git grep -l 'def sync_blocks' ./test/functional/*.py)
sed -i -e 's/def sync_blocks/def send_blocks/g' $FILE_LIST
sed -i -e 's/self.sync_blocks/self.send_blocks/g' $FILE_LIST
-END VERIFY SCRIPT-
```
Partial backport of core PR15773:
https://github.com/bitcoin/bitcoin/pull/15773/commits/fa4680ed0996a7c621265a34392c3eca827b2e48