Fix doc of PPFrame_Hash::cachedExpand

There is no PPNode_Hash class, use interface PPNode
Preprocessor_Hash does not work with DOMDocument, so remove that

Follow-Up: I621e9075e0f136ac188a4d2f53418b7cc957408d
Change-Id: Ic234d37e15b7fdf274bd55101bb576d2ec49a781
Merge "Fix doc of PPFrame_Hash::cachedExpand"