Simplify infix:<(+)>(**@p) candidate

With all of the necessary candidates and testing for them in place,
we can now do that

src/core/set_addition.pm

@@ -137,25 +137,10 @@ multi sub infix:<(+)>(Any $a, Any $b) {
     )
 }
 
-multi sub infix:<(+)>(**@p) is pure {
-    if Rakudo::Internals.ANY_DEFINED_TYPE(@p,Mixy) {
-        my $mixhash = nqp::istype(@p[0], MixHash)
-            ?? MixHash.new-from-pairs(@p.shift.pairs)
-            !! @p.shift.MixHash;
-        for @p.map(*.Mix(:view)) -> $mix {
-            $mixhash{$_} += $mix{$_} for $mix.keys;
-        }
-        $mixhash.Mix(:view);
-    }
-    else {  # go Baggy by default
-        my $baghash = nqp::istype(@p[0], BagHash)
-            ?? BagHash.new-from-pairs(@p.shift.pairs)
-            !! @p.shift.BagHash;
-        for @p.map(*.Bag(:view)) -> $bag {
-            $baghash{$_} += $bag{$_} for $bag.keys;
-        }
-        $baghash.Bag(:view);
-    }
+multi sub infix:<(+)>(**@p) {
+    my $result = @p.shift;
+    $result = $result (+) @p.shift while @p;
+    $result
 }
 
 # U+228E MULTISET UNION