Revert accidental default collector type change.

Default collector type had been changed to generational semi-space
by default by accident.

Change-Id: I060b3f292261b8bb258ca2a350e26a328340c49c
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 3cdf289..2af569a 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -401,8 +401,7 @@
   // Only the main GC thread, no workers.
   parsed->conc_gc_threads_ = 0;
   // Default is CMS which is Sticky + Partial + Full CMS GC.
-  // parsed->collector_type_ = gc::kCollectorTypeCMS;
-  parsed->collector_type_ = gc::kCollectorTypeGSS;
+  parsed->collector_type_ = gc::kCollectorTypeCMS;
   // If background_collector_type_ is kCollectorTypeNone, it defaults to the collector_type_ after
   // parsing options.
   parsed->background_collector_type_ = gc::kCollectorTypeNone;