Makefile: remove non-existent STAGING_DIR_TOOLCHAIN from dirclean

Makefile: remove non-existent STAGING_DIR_TOOLCHAIN from dirclean

Makefile: remove non-existent STAGING_DIR_TOOLCHAIN from dirclean

Openwrt's top level Makefile uses STAGING_DIR_TOOLCHAIN in the make dirclean
statement.
https://dev.openwrt.org/browser/trunk/Makefile#L55
    rm -rf $(STAGING_DIR) $(STAGING_DIR_HOST) $(STAGING_DIR_TOOLCHAIN)
$(TOOLCHAIN_DIR) $(BUILD_DIR_HOST) $(BUILD_DIR_TOOLCHAIN)

As far as I can determine, no such variable has been defined. I made a search
in Openwrt source repository and the one line in Makefile's dirclean command
is the only place where that variable exists.

The item has been introduced to Makefile by r8362, but even at that time
neither Makefile nor rules.mk defined such a variable. Most likely the goal
has been to set both staging_dir/toolchain and build_dir/toolchain to be
cleaned, but one of the variables has been erroneous. The correct variable
for build_dir/toolchain has been then added by r13494.

References:
https://dev.openwrt.org/changeset/8362/
https://dev.openwrt.org/browser/trunk/Makefile?rev=8362
https://dev.openwrt.org/browser/trunk/rules.mk?rev=8362
https://lists.openwrt.org/pipermail/openwrt-devel/2007-August/001159.html
https://dev.openwrt.org/changeset/13494

In current code,
    TOOLCHAIN_DIR = $(TOPDIR)/staging_dir/$(TOOLCHAIN_DIR_NAME)
    BUILD_DIR_TOOLCHAIN = $(TOPDIR)/build_dir/$(TOOLCHAIN_DIR_NAME)
so the item STAGING_DIR_TOOLCHAIN in the rm command is unnecessary.

signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45736 3c298f89-4303-0410-b956-a3cf2f4a3e73