Fix TClassEdit::IsDefAlloc

Fix a typo (consume key and value) and correct the algorithm
in the non-pair case (was forgetting to skip std:: consistently).

This solves ROOT-5999.
'Quick' fix for ROOT-5876 (and related issues)

If you feels like this is using a bandages to fix a leaking dam, you are likely correctly.

More technically, this avoid the routine that use GetInterpreterTypeName from re-expanding
the name (during the overly complex and obsolete scan through the list of possible names).

This avoids infinite recurse for vector<Long64_t> and map<Type,ABC_t>