dropbear: simplify rebuild on config changes

It's hard or even impossible to track affected sources
so it's safe to remove all built objects (if any).

Signed-off-by: Konstantin Demin <rockdrilla@gmail.com>

Author: rockdrilla

package/network/services/dropbear/Makefile

@@ -233,22 +233,15 @@ define Build/Configure/dropbear_headers
 	))
 endef
 
-define Build/Configure/dropbear_objects
-	grep -ERZl -e '($(subst $(space),|,$(strip $(sort $(patsubst !!%,%,$(foreach s,$(DB_OPT_COMMON) $(DB_OPT_CONFIG),$(word 1,$(subst $(comma),$(space),$(s)))))))))' \
-	$(PKG_BUILD_DIR)/ | sed -zE 's/^(.+)\.[^.]+$$$$/\1.o/' | sort -uV | xargs -0 -r rm -fv || :
-endef
-
 define Build/Configure
 	rm -f $(PKG_BUILD_DIR)/localoptions.h
 	$(Build/Configure/Default)
 
 	: > $(PKG_BUILD_DIR)/localoptions.h
 	$(Build/Configure/dropbear_headers)
 
-	# Enforce rebuild of files depending on configured options
-	$(Build/Configure/dropbear_objects)
-
-	# Rebuild them on config change
+	# Enforce rebuild
+	rm -rf $(PKG_BUILD_DIR)/obj
 	+$(MAKE) -C $(PKG_BUILD_DIR)/libtomcrypt clean
 	+$(MAKE) -C $(PKG_BUILD_DIR)/libtommath clean
 endef