tidy tmpdir logic

`mkdir -p` is already run elsewhere

Author: casperdcl

scripts/helpers.sh

@@ -65,10 +65,7 @@ command_exists() {
 
 get_tmp_dir() {
   local tmpdir="${TMPDIR:-${TMP:-${TEMP:-/tmp}}}"
-  if [ ! -d "$tmpdir" ]; then
-    local tmpdir=~/tmp
-    mkdir -p $tmpdir
-  fi
+  [ -d "$tmpdir" ] || local tmpdir=~/tmp
   echo "$tmpdir/tmux-$EUID-cpu"
 }