demos: update demos to the point where they run without warnings

Fixes jj-vcs#3209

demos/demo_juggle_conflicts.sh

@@ -14,7 +14,7 @@ new_tmp_dir
     echo "third" > file
     jj branch create third
     jj commit -m 'third'
-) >/dev/null
+) >/dev/null 2>&1
 
 comment "We are in a repo with three commits, all
 editing the same line:"
@@ -33,13 +33,13 @@ interesting is that the top commit has no conflict! That's because it
 has the changes from all three commits applied to it.
 
 Let's verify that by looking at its contents:"
-run_command "jj co second"
+run_command "jj new second"
 run_command "cat file"
 
 comment "Let's now instead make \"second\" and \"third\"
 sibling and merge them:"
 run_command "jj rebase -s second -d first"
-run_command "jj merge second third -m merged"
+run_command "jj new second third -m merged"
 run_command "jj log"
 comment "Again, because the merge commit has the
 changes from all three commits, it has no

demos/demo_operation_log.sh

@@ -6,9 +6,10 @@ new_tmp_dir
 {
     jj git clone https://github.com/octocat/Hello-World
     cd Hello-World
-    jj abandon octocat-patch-1
+    jj abandon --ignore-immutable octocat-patch-1@origin
     jj branch forget octocat-patch-1
-} > /dev/null
+    jj branch track test@origin
+} > /dev/null 2>&1
 
 comment "We are in the octocat/Hello-World repo.
 The \"operation log\" shows the operations
@@ -24,7 +25,7 @@ run_command "jj rebase -d test"
 
 comment "We are now going to make another change off of
 master:"
-run_command "jj co master"
+run_command "jj new master"
 run_command "jj describe -m \"other stuff\""
 
 comment "The repo now looks like this:"

demos/demo_resolve_conflicts.sh

@@ -6,9 +6,9 @@ new_tmp_dir
 {
     jj git clone https://github.com/octocat/Hello-World 
     cd Hello-World
-    jj abandon test
+    jj abandon --ignore-immutable test@origin
     jj branch forget test
-} > /dev/null
+} > /dev/null 2>&1
 
 comment "We are on the master branch of the
 octocat/Hello-World repo:"

demos/demo_working_copy.sh

@@ -6,11 +6,11 @@ new_tmp_dir
 {
     jj git clone https://github.com/octocat/Hello-World
     cd Hello-World
-    jj abandon test
+    jj abandon --ignore-immutable test@origin
     jj branch forget test
-    jj abandon octocat-patch-1
+    jj abandon --ignore-immutable octocat-patch-1@origin
     jj branch forget octocat-patch-1
-}> /dev/null
+}> /dev/null 2>&1
 
 comment "We are in the octocat/Hello-World repo.
 We have an empty working copy on top of master:"
@@ -31,7 +31,7 @@ run_command "jj branch create goodbye"
 run_command "jj log"
 
 comment "Start working on a new change off of master:"
-run_command "jj co master"
+run_command "jj new master"
 comment "Note that we were told the working copy is now empty (AKA clean). The
 \"goodbye\" change stayed in its own commit:"