mongoose: drop unused MONGOOSE_NO_DL define

This define is not used anywhere in the mongoose sources since v6.0 (commit
8927c9d22b3f), so drop it.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mongoose/mongoose.mk

@@ -10,7 +10,7 @@ MONGOOSE_LICENSE = GPL-2.0
 MONGOOSE_LICENSE_FILES = LICENSE
 MONGOOSE_INSTALL_STAGING = YES
 
-MONGOOSE_CFLAGS = $(TARGET_CFLAGS) $(TARGET_LDFLAGS) -DMONGOOSE_NO_DL
+MONGOOSE_CFLAGS = $(TARGET_CFLAGS) $(TARGET_LDFLAGS)
 
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 MONGOOSE_DEPENDENCIES += openssl