imagebuilder: remove existing root filesystem images

Reduces tarball size and improves build time

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

target/imagebuilder/Makefile

@@ -66,6 +66,7 @@ endif
 		$(PKG_BUILD_DIR)/target/linux/*/patches{,-*}
 	-cp $(KERNEL_BUILD_DIR)/* $(IB_KDIR)/ # don't copy subdirectories here
 	-cp $(LINUX_DIR)/.config $(IB_LDIR)/
+	rm -f $(IB_KDIR)/root.*
 	if [ -x $(LINUX_DIR)/scripts/dtc/dtc ]; then \
 		$(INSTALL_DIR) $(IB_LDIR)/scripts/dtc; \
 		$(INSTALL_BIN) $(LINUX_DIR)/scripts/dtc/dtc $(IB_LDIR)/scripts/dtc/dtc; \