Revert "Revert "Add one LinearAlloc per ClassLoader""

Issue was fixed by:
https://android-review.googlesource.com/#/c/171945/

Bug: 22720414

This reverts commit 7de5dfe37f3cf24e1166412b589f6f67dcd1f1c0.
diff --git a/runtime/gc/collector/semi_space.cc b/runtime/gc/collector/semi_space.cc
index ed63ed0..7f57f30 100644
--- a/runtime/gc/collector/semi_space.cc
+++ b/runtime/gc/collector/semi_space.cc
@@ -248,6 +248,7 @@
     ReaderMutexLock mu(self_, *Locks::heap_bitmap_lock_);
     SweepSystemWeaks();
   }
+  Runtime::Current()->GetClassLinker()->CleanupClassLoaders();
   // Revoke buffers before measuring how many objects were moved since the TLABs need to be revoked
   // before they are properly counted.
   RevokeAllThreadLocalBuffers();