t/op/signatures.t: Nuke the tests of modifying @_ during signature argument processing

The specific behaviour of this obscure modification case is not
documented or relied upon elsewhere in code. Rather than attempt to
preserve this cornercase, it's easier just to no longer test for it, as
upcoming changes will alter the values that are visible.

Author: leonerd

t/op/signatures.t

@@ -1399,20 +1399,8 @@ is scalar(t145()), undef;
     }
     is ref(t149()), "ARRAY", "t149: closure can make new lexical a ref";
 
-    # Quiet the 'use of @_ is experimental' warnings
-    no warnings 'experimental::args_array_with_signatures';
-
-    sub t150 ($a = do {@_ = qw(a b c); 1}, $b = 2) {
-        is $a, 1,   "t150: a: growing \@_";
-        is $b, "b", "t150: b: growing \@_";
-    }
-    t150();
-
-    sub t151 ($a = do {tie @_, 'Tie::StdArray'; @_ = qw(a b c); 1}, $b = 2) {
-        is $a, 1,   "t151: a: tied \@_";
-        is $b, "b", "t151: b: tied \@_";
-    }
-    t151();
+    # Tests t150, t151, t156 to t159 were related to modifying @_ during
+    # signature handling. This is no longer supported
 
     sub t152 ($a = t152x(), @b) {
         sub t152x { @b = qw(a b c); 1 }
@@ -1438,30 +1426,6 @@ is scalar(t145()), undef;
     }
     is t155(), "1-", "t155: closure can make new lexical hash tied";
 
-    sub t156 ($a = do {@_ = qw(a b c); 1}, @b) {
-        is $a, 1,       "t156: a: growing \@_";
-        is "@b", "b c", "t156: b: growing \@_";
-    }
-    t156();
-
-    sub t157 ($a = do {@_ = qw(a b c); 1}, %b) {
-        is $a, 1,                     "t157: a: growing \@_";
-        is join(':', sort %b), "b:c", "t157: b: growing \@_";
-    }
-    t157();
-
-    sub t158 ($a = do {tie @_, 'Tie::StdArray'; @_ = qw(a b c); 1}, @b) {
-        is $a, 1,          "t158: a: tied \@_";
-        is "@b", "b c",    "t158: b: tied \@_";
-    }
-    t158();
-
-    sub t159 ($a = do {tie @_, 'Tie::StdArray'; @_ = qw(a b c); 1}, %b) {
-        is  $a, 1,                     "t159: a: tied \@_";
-        is  join(':', sort %b), "b:c", "t159: b: tied \@_";
-    }
-    t159();
-
     # see if we can handle the equivalent of @a = ($a[1], $a[0])
 
     sub t160 ($s, @a) {