jj: Switch manual commit splitting alias to use split

Currently `ji` (for jj insert) does a 'manual' `jj split` by creating an
empty commit underneath, squasing interactively and then moving back to
the original. All of that is done by the existing `jj split` command.

So we simply use it. I am keeping the `ji` alias for now, could still be
'jj insert' or 'jj spl(I)t' I suppose.

vcs/jj/config/sh/alias.d/jj.sh

@@ -36,9 +36,8 @@ alias jsi="jj squash --interactive"
 
 # oops buttons
 alias ju="jj undo"
-# for damn,-forgot-to-split-this-commit workflow
-# Creates a new commit before with your selected changes, lets you describe it and carry on
-alias ji="jj new -B@ --no-edit && jj squash --interactive && jj edit '@-' && jj describe && jj edit '@+'"
+# allows you to split the current change into multiple
+alias ji="jj split"
 
 # revset info
 alias jl="jj log -T builtin_log_oneline"