Outcomment reattach-to-user-namespace part in .tmux.conf

This seems to be not necessary anymore [1]. This also gets rid of the need
to install reattach-to-user-namespace with Homebrew.

[1] tmux-plugins/tmux-sensible#42

Author: weibeld

.tmux.conf

@@ -21,13 +21,16 @@ set    -sg escape-time          1
 set    -g  base-index           1
 setw   -g  pane-base-index      1
 
+# This seems to be not necessary anymore, see [1].
+# [1] https://github.com/tmux-plugins/tmux-sensible/issues/42
+#
 # Mac only: fix for bug that in newer Mac versions (10.10, 10.11, etc.) prevents
 # "$ open xyz.pdf" and "$ subl xyz.txt" from working. The error in each case has
 # something to do with a windows server.
 # This requires "$ brew install reattach-to-user-namespace", see explanation on
 # http://www.elmund.io/osx/2015/07/10/open-command-in-osx-tmux/
-if-shell "uname | grep -q Darwin" \
-  "set -g default-command \"reattach-to-user-namespace -l ${SHELL}\""
+#if-shell "uname | grep -q Darwin" \
+#  "set -g default-command \"reattach-to-user-namespace -l ${SHELL}\""
 
 #------------------------------------------------------------------------------#
 # Key bindings