kernel: prevent adding custom string to localversion

When the kernel build picks up a localversion file in the source tree,
that string is unconditionally appended to LOCALVERSION and affects the
uname string.
Make sure to delete any such file.

Signed-off-by: Josua Mayer <josua.mayer97@gmail.com>

include/kernel-defaults.mk

@@ -111,6 +111,7 @@ define Kernel/SetNoInitramfs
 endef
 
 define Kernel/Configure/Default
+	rm -f $(LINUX_DIR)/localversion
 	$(LINUX_CONF_CMD) > $(LINUX_DIR)/.config.target
 # copy CONFIG_KERNEL_* settings over to .config.target
 	awk '/^(#[[:space:]]+)?CONFIG_KERNEL/{sub("CONFIG_KERNEL_","CONFIG_");print}' $(TOPDIR)/.config >> $(LINUX_DIR)/.config.target