Makefile.install: rm unused vars/target

1. LOGROTATEDIR is not used since commit f4e9a1df
("make: don't install service and logrotate configs").

2. SYSTEMDUNITDIR is not used since commit 10d5e9a4
("criu: scripts: remove criu service files").

3. install-tree target was *never* used, makes no sense
to keep it.

While at it, also
 - sort the variables in "export" statement to match
   the order of appearance in Makefile;

 - don't export DESTDIR (it is exported by default as
   it always comes from the make command line);

 - remove unused variable from INSTALL.md.

travis-ci: success for Makefile.install fixes
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

INSTALL.md

@@ -13,7 +13,6 @@ this command accepts the following variables:
  * **BINDIR**, to specify where to put CRIT tool (`$(PREFIX)/bin` by default);
  * **SBINDIR**, to specify where to put CRIU executable (`$(PREFIX)/sbin` by default);
  * **MANDIR**, to specify directory for manual pages (`$(PREFIX)/share/man` by default);
- * **SYSTEMDUNITDIR**, to specify place where systemd units are living (`$(PREFIX)/lib/systemd/system` by default);
  * **LIBDIR**, to specify directory where to put libraries (guess the correct path  by default).
 
 Thus one can type

Makefile.install

@@ -4,8 +4,6 @@ PREFIX		:= /usr/local
 BINDIR		:= $(PREFIX)/bin
 SBINDIR		:= $(PREFIX)/sbin
 MANDIR		:= $(PREFIX)/share/man
-SYSTEMDUNITDIR	:= $(PREFIX)/lib/systemd/system
-LOGROTATEDIR	:= $(PREFIX)/etc/logrotate.d
 LIBDIR		:= $(PREFIX)/lib
 INCLUDEDIR	:= $(PREFIX)/include
 LIBEXECDIR	:= $(PREFIX)/libexec
@@ -23,15 +21,8 @@ else
         endif
 endif
 
-export BINDIR SBINDIR MANDIR SYSTEMDUNITDIR LOGROTATEDIR
-export INCLUDEDIR LIBDIR DESTDIR PREFIX LIBEXECDIR
-
-install-tree:
-	$(Q) mkdir -p $(DESTDIR)$(SYSTEMDUNITDIR)
-	$(Q) mkdir -p $(DESTDIR)$(LOGROTATEDIR)
-	$(Q) mkdir -p $(DESTDIR)$(INCLUDEDIR)
-	$(Q) mkdir -p $(DESTDIR)$(LIBEXECDIR)
-.PHONY: install-tree
+export PREFIX BINDIR SBINDIR MANDIR
+export LIBDIR INCLUDEDIR LIBEXECDIR
 
 install-man:
 	$(Q) $(MAKE) -C Documentation install