Revert invalid fn return type parsing change

Fix #78507.

src/test/ui/parser/issue-24780.rs

@@ -1,8 +1,8 @@
 // Verify that '>' is not both expected and found at the same time, as it used
 // to happen in #24780. For example, following should be an error:
-// expected one of ..., `>`, ... found `>`. No longer exactly this, but keeping for posterity.
+// expected one of ..., `>`, ... found `>`.
 
-fn foo() -> Vec<usize>> { //~ ERROR unmatched angle bracket
+fn foo() -> Vec<usize>> { //~ ERROR expected one of `!`, `+`, `::`, `;`, `where`, or `{`, found `>`
     Vec::new()
 }
 

src/test/ui/parser/issue-24780.stderr

@@ -1,8 +1,8 @@
-error: unmatched angle bracket
+error: expected one of `!`, `+`, `::`, `;`, `where`, or `{`, found `>`
   --> $DIR/issue-24780.rs:5:23
    |
 LL | fn foo() -> Vec<usize>> {
-   |                       ^^ help: remove extra angle bracket
+   |                       ^ expected one of `!`, `+`, `::`, `;`, `where`, or `{`
 
 error: aborting due to previous error