In MVMLexicalRegistry, lexreg[i]->value is always i.

The value *is* the index in the array - it's used to find the correct array
index when doing a hash lookup by name. Hence use the `i` directly,
avoiding a dereference.

This code was initially in src/6model/reprs/MVMIter.c, added in Oct 2015
by commit 5075f5b:
    Make context iterator include values.

    Before it just had keys, but skipped the values, menaing that things
    like CORE::.values in Rakudo just gave a load of (Mu).

`lexreg[i]->value` was always `i` back then too, so it's been a tiny bit
Less Than Optimal since day 1.

src/spesh/frame_walker.c

@@ -342,7 +342,7 @@ MVMObject * MVM_spesh_frame_walker_get_lexicals_hash(MVMThreadContext *tc, MVMSp
         MVMuint32 i;
         for (i = 0; i < sf->body.num_lexicals; i++) {
             MVMuint16 type = sf->body.lexical_types[i];
-            MVMuint32 idx = base_index + lexreg[i]->value;
+            MVMuint32 idx = base_index + i;
             switch (type) {
                 case MVM_reg_obj: {
                     MVMObject *obj = frame->env[idx].o;