stubby: clean up the makefile

These cmake modules are actually never referenced. Stubby itself doesn't link to
libidn or libunbound, only getdns does. They're most likely leftovers from when
stubby was split from getdns to its own repository.

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

net/stubby/Makefile

@@ -6,7 +6,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=stubby
 PKG_VERSION:=0.4.0
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://github.com/getdnsapi/$(PKG_NAME)
@@ -45,11 +45,6 @@ define Package/stubby/conffiles
 /etc/config/stubby
 endef
 
-define Build/Prepare
-	$(call Build/Prepare/Default)
-	rm $(PKG_BUILD_DIR)/cmake/modules/FindLibidn2.cmake $(PKG_BUILD_DIR)/cmake/modules/FindLibunbound.cmake
-endef
-
 define Package/stubby/install
 	$(INSTALL_DIR) $(1)/usr/sbin
 	$(INSTALL_BIN) $(PKG_INSTALL_DIR)/usr/bin/stubby $(1)/usr/sbin/stubby