Cleanup way elidable types are determined.

After adding the pointer type, it didn't make sense for elidable types
to be specified in canElideCallback. Now the decision as to whether a
specific type is elidable has been moved into 'isElidableType' on the
Type class.

Bug: 33298401
Test: mma in hardware/interfaces
Change-Id: I66cbaed4c533013a52e59fc8e7edcdabc9ab9f20
diff --git a/PointerType.h b/PointerType.h
index 242cc63..cd0f839 100644
--- a/PointerType.h
+++ b/PointerType.h
@@ -27,6 +27,8 @@
 
     bool isPointer() const override;
 
+    bool isElidableType() const override;
+
     void addNamedTypesToSet(std::set<const FQName> &set) const override;
 
     std::string getCppType(