Change iftable to never be null

Simplifies code generation by removing a null check. The null case
is rare.

Ritzperf code size: 13107624 -> 13095336

Also addressed comments from previous CL.

Bug: 32577579

Test: test-art-host, run ritzperf both with CC

Change-Id: I2b31e800867112869d7f0643e16c08826296979e
diff --git a/runtime/class_table.h b/runtime/class_table.h
index bc9eaf4..558c144 100644
--- a/runtime/class_table.h
+++ b/runtime/class_table.h
@@ -48,7 +48,7 @@
     uint32_t operator()(const GcRoot<mirror::Class>& root) const NO_THREAD_SAFETY_ANALYSIS;
     // Same class loader and descriptor.
     bool operator()(const GcRoot<mirror::Class>& a, const GcRoot<mirror::Class>& b) const
-        NO_THREAD_SAFETY_ANALYSIS;;
+        NO_THREAD_SAFETY_ANALYSIS;
     // Same descriptor.
     bool operator()(const GcRoot<mirror::Class>& a, const char* descriptor) const
         NO_THREAD_SAFETY_ANALYSIS;