Make ScopedAssertNoThreadSuspension no overhead for non-debug

Previously it required Thread::Current() which may not be free.
The plan is to add a lot more ScopedAssertNoThreadSuspension in
the codebase.

Also cleaned up callers.

Bug: 31458474
Change-Id: I5a1621a5435476504d22266cc01a9bf26aab7568
diff --git a/runtime/art_method.cc b/runtime/art_method.cc
index 1392399..82f8edf 100644
--- a/runtime/art_method.cc
+++ b/runtime/art_method.cc
@@ -107,7 +107,7 @@
 }
 
 bool ArtMethod::HasSameNameAndSignature(ArtMethod* other) {
-  ScopedAssertNoThreadSuspension ants(Thread::Current(), "HasSameNameAndSignature");
+  ScopedAssertNoThreadSuspension ants("HasSameNameAndSignature");
   const DexFile* dex_file = GetDexFile();
   const DexFile::MethodId& mid = dex_file->GetMethodId(GetDexMethodIndex());
   if (GetDexCache() == other->GetDexCache()) {