Fixup clippy tests

Don't depend on the fact that `!` falls back to `()` and so panic-ish things
can be used in `-> impl ImplementedForUnit` functions

Author: WaffleLapkin

src/tools/clippy/tests/ui/new_ret_no_self.rs

@@ -390,9 +390,7 @@ mod issue7344 {
 
     impl<T> RetImplTraitSelf2<T> {
         // should not trigger lint
-        fn new(t: T) -> impl Trait2<(), Self> {
-            unimplemented!()
-        }
+        fn new(t: T) -> impl Trait2<(), Self> {}
     }
 
     struct RetImplTraitNoSelf2<T>(T);
@@ -401,7 +399,6 @@ mod issue7344 {
         // should trigger lint
         fn new(t: T) -> impl Trait2<(), i32> {
             //~^ ERROR: methods called `new` usually return `Self`
-            unimplemented!()
         }
     }
 

src/tools/clippy/tests/ui/new_ret_no_self.stderr

@@ -96,11 +96,10 @@ LL | |         }
    | |_________^
 
 error: methods called `new` usually return `Self`
-  --> tests/ui/new_ret_no_self.rs:402:9
+  --> tests/ui/new_ret_no_self.rs:400:9
    |
 LL | /         fn new(t: T) -> impl Trait2<(), i32> {
 LL | |
-LL | |             unimplemented!()
 LL | |         }
    | |_________^