build: make <subdir>/install opt-in, use it for target/ only

Fixes buildbot errors on running make target/install or
toolchain/install

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/Makefile

@@ -12,7 +12,6 @@ include $(INCLUDE_DIR)/rootfs.mk
 -include $(TMP_DIR)/.packagedeps
 $(curdir)/autoremove:=1
 $(curdir)/builddirs:=$(sort $(package-) $(package-y) $(package-m))
-$(curdir)/builddirs-install:=.
 $(curdir)/builddirs-default:=. $(sort $(package-y) $(package-m))
 $(curdir)/builddirs-prereq:=. $(sort $(prereq-y) $(prereq-m))
 ifdef CHECK_ALL