Revert "prevent recursion in %_defconfig rules"

This reverts commit 94dd02f5d0ce89549a82a99c56602e1c4a73bae7.

The change breaks defconfigs from BR2_EXTERNAL, both for in-tree and
out-of-tree builds.

Besides, the problem reported in 94dd02f could not be reproduced.

I can read French, and I suspect a relative path was used for either
BR2_EXTERNAL or O.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Jérémy Rosen <jeremy.rosen@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -762,14 +762,10 @@ defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< --defconfig=$(TOPDIR)/configs/$@ $(CONFIG_CONFIG_IN)
 
-$(TOPDIR)/configs/%_defconfig:;
-
 %_defconfig: $(BUILD_DIR)/buildroot-config/conf $(BR2_EXTERNAL)/configs/%_defconfig outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< --defconfig=$(BR2_EXTERNAL)/configs/$@ $(CONFIG_CONFIG_IN)
 
-$(BR2_EXTERNAL)/configs/%_defconfig:;
-
 savedefconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< \