[lldb][NFC] Rewrite python_api/rdar-12481949 test

Summary:
This renames the test `rdar-12481949` to `get-value-32bit-int` as it just tests that we return the
correct result get calling GetValueAsSigned/GetValueAsUnsigned on 32-bit integers.

It also deletes all the strange things going on in this test including resetting the data formatters (which are to my
knowledge not used to calculate scalar values) and testing Python's long integers (let's just assume that our Python
distribution works correctly). Also modernises the setup code.

Reviewers: labath, aprantl

Reviewed By: aprantl

Subscribers: JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D72593