Remove now unreachable parse recovery code

StructLiteralNeedingParens is no longer reachable always giving
precedence to StructLiteralNotAllowedHere.

As an aside: The former error struct shouldn't've existed in the
first place. We should've just used the latter in this branch.

compiler/rustc_parse/src/parser/expr.rs

@@ -2296,7 +2296,7 @@ impl<'a> Parser<'a> {
             });
         }
 
-        let (attrs, blk) = self.parse_block_common(lo, blk_mode, true, None)?;
+        let (attrs, blk) = self.parse_block_common(lo, blk_mode, None)?;
         Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
     }