No longer require experimental for $*COLLATION.set

Per https://colabti.org/irclogger/irclogger_log/perl6-dev?date=2018-10-28#l108

lib/experimental.pm6

@@ -193,7 +193,12 @@ package EXPORT::pack {
 }
 
 package EXPORT::collation {
-    OUR::<EXPERIMENTAL-COLLATION> := True;
+    # this is no longer experimental, but keep the package to prevent
+    # code that caters to this and earlier versions of compilers from
+    # breaking
+    #
+    # XXX TODO: should be fine to remove on 2019-12. There is also a test
+    # in t/02-rakudo/99-misc.t that will need to be removed too at the time
 }
 
 # vim: ft=perl6 expandtab sw=4

src/core/Collation.pm6

@@ -12,10 +12,6 @@ class Collation {
         Int :$tertiary   = 1,
         Int :$quaternary = 1)
     {
-        nqp::isnull(nqp::getlexcaller('EXPERIMENTAL-COLLATION')) and X::Experimental.new(
-            feature => 'the $*COLLATION dynamic variable',
-            use     => 'collation'
-        ).throw;
         my int $i = 0;
         $i += 1   if $primary.sign    ==  1;
         $i += 2   if $primary.sign    == -1;

t/02-rakudo/99-misc.t

@@ -2,7 +2,7 @@ use lib <t/packages/>;
 use Test;
 use Test::Helpers;
 
-plan 7;
+plan 8;
 
 subtest '.lang-ver-before method on Perl6::World' => {
     plan 5;
@@ -135,3 +135,13 @@ subtest 'postfix-to-prefix-inc-dec opt does not rewrite custom ops' => {
     is-deeply @res, [<a a b b>],
         'regex blocks update their lexical variables right';
 }
+
+group-of 2 => 'collation experiment' => {
+    is-run ｢$*COLLATION.set: :primary; print 'pass'｣,
+        :out<pass>, '$*COLLECTION.set no longer requires experimental pragma';
+    is-run ｢
+        use experimental :collation;
+        $*COLLATION.set: :primary;
+        print 'pass'
+    ｣, :out<pass>, 'we can still use the pragma (to support old code)';
+}