Revert "[perl #119043] Exempt shared hash key consts from ro"

This reverts commit ba36554e02872e48d146177a57a9cfb154727fae.

It turns out it reinstates bugs like this:

$ perl -e 'for(1..10){for(__PACKAGE__){warn $_; $_++}}'
main at -e line 1.
maio at -e line 1.
maip at -e line 1.
maiq at -e line 1.
mair at -e line 1.
mais at -e line 1.
mait at -e line 1.
maiu at -e line 1.
maiv at -e line 1.
maiw at -e line 1.

1 files changed, 4 insertions, 3 deletions

diff --git a/lib/overload.t b/lib/overload.t
index e9ceb50b1e..3af969bc69 100644
--- a/lib/overload.t
+++ b/lib/overload.t
@@ -1293,15 +1293,16 @@ foreach my $op (qw(<=> == != < <= > >=)) {
 }
 
 {
-    # Check readonliness of constants (brought up in bug #109744)
-    # For historical reasons, shared hash key scalars are exempt
+    # Check readonliness of constants, whether shared hash key
+    # scalars or no (brought up in bug #109744)
     BEGIN { overload::constant integer => sub { "main" }; }
     eval { ${\5} = 'whatever' };
     like $@, qr/^Modification of a read-only value attempted at /,
 	'constant overloading makes read-only constants';
     BEGIN { overload::constant integer => sub { __PACKAGE__ }; }
     eval { ${\5} = 'whatever' };
-    is $@, "", 'except with shared hash key scalars';
+    like $@, qr/^Modification of a read-only value attempted at /,
+	'... even with shared hash key scalars';
 }
 
 {