Remove blanket silencing of "type annotation needed" errors

Remove blanket check for existence of other errors before emitting
"type annotation needed" errors, and add some eager checks to avoid
adding obligations when they refer to types that reference
`[type error]` in order to reduce unneded errors.

src/test/ui/traits/trait-static-method-generic-inference.rs

@@ -22,7 +22,7 @@ mod base {
 
 pub fn foo() {
     let _f: base::Foo = base::HasNew::new();
-    //~^ ERROR type annotations required
+    //~^ ERROR type annotations needed
 }
 
 fn main() { }