Remove send-keys -l support check as it is not needed

After some experimentation it turns out that if input to send-keys is
not a known key sequence like `C-m` or `C-l` for example, it it
automatically treated as literal input.

 Negating the need to use it and hence check if it's supported.

lib/layout-helpers.sh

@@ -68,12 +68,7 @@ select_pane() {
 #   - $2: (optional) Target pane ID to run command in.
 #
 run_cmd() {
-  literal_support=$(tmux send-keys -l 2&> /dev/null ; echo $?)
-  if [ $literal_support -eq 0 ]; then
-    tmux send-keys -t "$session:$window.$2" -l "$1"
-  else
-    tmux send-keys -t "$session:$window.$2" "$1"
-  fi
+  tmux send-keys -t "$session:$window.$2" "$1"
   tmux send-keys -t "$session:$window.$2" "C-m"
 }