tests: remove few ignore-stage2

beta was branched long ago, so can be removed

Author: klensy

tests/ui/codemap_tests/huge_multispan_highlight.rs

@@ -1,7 +1,5 @@
 //@ compile-flags: --error-format=human --color=always
 //@ ignore-windows
-// Temporary until next release:
-//@ ignore-stage2
 fn main() {
     let _ = match true {
         true => (

tests/ui/codemap_tests/huge_multispan_highlight.svg

@@ -1,6 +1,4 @@
 //@ check-pass
 //@ ignore-windows
 //@ compile-flags: -Cremark=foo --error-format=human --color=always
-// Temporary until next release:
-//@ ignore-stage2
 fn main() {}

tests/ui/diagnostic-flags/colored-session-opt-error.rs

@@ -3,8 +3,6 @@
 //@ compile-flags: --error-format=human --color=always
 //@ error-pattern:for<'a> 
 //@ edition:2018
-// Temporary until next release:
-//@ ignore-stage2
 
 use core::pin::Pin;
 use core::future::Future;

tests/ui/error-emitter/highlighting.rs

@@ -1,7 +1,5 @@
 //@ compile-flags: --error-format=human --color=always
 //@ error-pattern: missing lifetime specifier
-// Temporary until next release:
-//@ ignore-stage2
 
 fn short(foo_bar: &Vec<&i32>) -> &i32 {
     &12