Revert "Add WithResolverUserOptions for custom resolver build options" (#1839)

This reverts commit ff1be3fcc57773d500921fad479d82ec171e2358.

resolver/resolver.go

@@ -90,9 +90,6 @@ type Address struct {
 // BuildOption includes additional information for the builder to create
 // the resolver.
 type BuildOption struct {
-	// UserOptions can be used to pass configuration between DialOptions and the
-	// resolver.
-	UserOptions interface{}
 }
 
 // ClientConn contains the callbacks for resolver to notify any updates