[lldb] Delete ValueObject::GetBaseClassPath

Summary:
This method has exactly one call site, which is only actually executed
if `ValueObject::IsBaseClass` returns false. However, the first thing
that `ValueObject::GetBaseClassPath` does is check if `ValueObject::IsBaseClass`
is true. Because this can never be the case, this method always returns false
and is therefore effectively dead.

Differential Revision: https://reviews.llvm.org/D73517