8025855: Simplify GenRemSet code slightly

Summary: Remove a few redundant switch-statements
Reviewed-by: jcoomes, tschatzl

src/share/vm/memory/collectorPolicy.cpp

@@ -137,15 +137,8 @@ bool CollectorPolicy::use_should_clear_all_soft_refs(bool v) {
 
 GenRemSet* CollectorPolicy::create_rem_set(MemRegion whole_heap,
                                            int max_covered_regions) {
-  switch (rem_set_name()) {
-  case GenRemSet::CardTable: {
-    CardTableRS* res = new CardTableRS(whole_heap, max_covered_regions);
-    return res;
-  }
-  default:
-    guarantee(false, "unrecognized GenRemSet::Name");
-    return NULL;
-  }
+  assert(rem_set_name() == GenRemSet::CardTable, "unrecognized GenRemSet::Name");
+  return new CardTableRS(whole_heap, max_covered_regions);
 }
 
 void CollectorPolicy::cleared_all_soft_refs() {

src/share/vm/memory/genRemSet.cpp

@@ -32,13 +32,8 @@
 // enumeration.)
 
 uintx GenRemSet::max_alignment_constraint(Name nm) {
-  switch (nm) {
-  case GenRemSet::CardTable:
-    return CardTableRS::ct_max_alignment_constraint();
-  default:
-    guarantee(false, "Unrecognized GenRemSet type.");
-    return (0); // Make Windows compiler happy
-  }
+  assert(nm == GenRemSet::CardTable, "Unrecognized GenRemSet type.");
+  return CardTableRS::ct_max_alignment_constraint();
 }
 
 class HasAccumulatedModifiedOopsClosure : public KlassClosure {