remove old irrelevant USER_ARDOUR_DIR in start-up script

It should have been XDG_CONFIG_HOME and ardour4, anyway.
Ardour4 checks for config dirs, allows to import A3 config and
also handles the case if the dir can't be created itself.

tools/linux_packaging/ardour.sh.in

@@ -25,11 +25,6 @@ BIN_DIR=$(dirname $(readlink -f $0))
 INSTALL_DIR=$(dirname $BIN_DIR)
 LIB_DIR=$INSTALL_DIR/lib
 ETC_DIR=$INSTALL_DIR/etc
-USER_ARDOUR_DIR=$HOME/.config/ardour3
-
-if [ ! -d $USER_ARDOUR_DIR ] ; then
-    mkdir -p $USER_ARDOUR_DIR || exit 1
-fi
 
 # this triggers code in main() that will reset runtime environment variables
 # to point to directories inside the ardour package