remove unused constant preal_of_rat; remove several unused lemmas about preals
remove unused constant preal_of_rat; remove several unused lemmas about preals

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle