@kracovwolf I think you will want to use “Search Replace” with “Search Mode” of “Regular Expression”.
This is a very complicated option, but what you specifically need to do is simple:
^J
means “J at the start of a line” in Regular Expression language. You can replace this with nothing. From your example, you should replace “J space” which is also there.
It will not remove the start of line. It will only remove J or remove J space.
J$
means “J at the end of a line”.
Doing one and then the other is simplest.
It will still be your responsibility to not remove more J s than you want to.