emacs: Remove outdated references to ~ in tests

Author: tomjakubowski

src/etc/emacs/rust-mode-tests.el

@@ -301,7 +301,7 @@ struct Foo { bar: int,
 
 struct Blah {x:int,
              y:int,
-             z:~str}"))
+             z:String"))
 
 (ert-deftest indent-doc-comments ()
   (test-indent
@@ -331,7 +331,7 @@ struct foo {
     b:char
 }
 
-fn bar(x:~int) {   // comment here should not affect the next indent
+fn bar(x:Box<int>) {   // comment here should not affect the next indent
     bla();
     bla();
 }"))
@@ -387,7 +387,7 @@ fn baz(   a:int,  // shoudl work with a comment here
    "
 fn args_on_the_next_line( // with a comment
     a:int,
-    b:~str) {
+    b:String) {
     let aaaaaa = [
         1,
         2,