Remove explicit fail in new command

That fail prevents the real error message from being displayed

rc/windowing/new-client.kak

@@ -3,10 +3,6 @@ new [<commands>]: create a new Kakoune client
 The ''terminal'' alias is being used to determine the user''s preferred terminal emulator
 The optional arguments are passed as commands to the new client' \
 %{
-    try %{
     terminal kak -c %val{session} -e "%arg{@}"
-    } catch %{
-        fail "The 'terminal' alias must be defined to use this command"
-    }
 }