Update NLL tests

src/test/ui/rfc-2005-default-binding-mode/borrowck-issue-49631.nll.stderr

@@ -5,7 +5,7 @@ LL |     while let Some(Ok(string)) = foo.get() {
    |                                  --- immutable borrow occurs here
 LL |         foo.mutate();
    |         ^^^^^^^^^^^^ mutable borrow occurs here
-LL |         //~^ ERROR cannot borrow `foo` as mutable
+LL |
 LL |         println!("foo={:?}", *string);
    |                              ------- immutable borrow later used here
 

src/test/ui/rfc-2005-default-binding-mode/enum.nll.stderr

@@ -1,19 +1,19 @@
 error[E0594]: cannot assign to `*x` which is behind a `&` reference
   --> $DIR/enum.rs:9:5
    |
-LL |     *x += 1; //~ ERROR cannot assign to immutable
+LL |     *x += 1;
    |     ^^^^^^^ `x` is a `&` reference, so the data it refers to cannot be written
 
 error[E0594]: cannot assign to `*x` which is behind a `&` reference
   --> $DIR/enum.rs:13:9
    |
-LL |         *x += 1; //~ ERROR cannot assign to immutable
+LL |         *x += 1;
    |         ^^^^^^^ `x` is a `&` reference, so the data it refers to cannot be written
 
 error[E0594]: cannot assign to `*x` which is behind a `&` reference
   --> $DIR/enum.rs:19:9
    |
-LL |         *x += 1; //~ ERROR cannot assign to immutable
+LL |         *x += 1;
    |         ^^^^^^^ `x` is a `&` reference, so the data it refers to cannot be written
 
 error: aborting due to 3 previous errors

src/test/ui/rfc-2005-default-binding-mode/explicit-mut.nll.stderr

@@ -1,19 +1,19 @@
 error[E0594]: cannot assign to `*n` which is behind a `&` reference
   --> $DIR/explicit-mut.rs:7:13
    |
-LL |             *n += 1; //~ ERROR cannot assign to immutable
+LL |             *n += 1;
    |             ^^^^^^^ `n` is a `&` reference, so the data it refers to cannot be written
 
 error[E0594]: cannot assign to `*n` which is behind a `&` reference
   --> $DIR/explicit-mut.rs:15:13
    |
-LL |             *n += 1; //~ ERROR cannot assign to immutable
+LL |             *n += 1;
    |             ^^^^^^^ `n` is a `&` reference, so the data it refers to cannot be written
 
 error[E0594]: cannot assign to `*n` which is behind a `&` reference
   --> $DIR/explicit-mut.rs:23:13
    |
-LL |             *n += 1; //~ ERROR cannot assign to immutable
+LL |             *n += 1;
    |             ^^^^^^^ `n` is a `&` reference, so the data it refers to cannot be written
 
 error: aborting due to 3 previous errors