[analyzer][NFC] Remove irrelevant overcomplicated test (#147536)

This commit removes the test file test-member-invalidation.cpp which was
recently introduced in 39bc0529b018a89b4b6a21aaabe240cd3a65c44d by
splitting off a test case from new.cpp.

In that commit I preserved that test in a slightly modified setting to
demonstrate that it wasn't broken by the change; but in this separate
commit I'm removing it because I don't think that it "deserves a place"
among our tests.

The primary issue is that this test examines the values of data members
of a deleted object -- which is irrelevant, because code that relies on
the value of these members should be reported as a use-after-free bug.
(In fact, cplusplus.NewDelete reports it as a use-after-free bug, and
the checker family `MallocChecker` sinks the execution path even if that
particular frontend is not enabled.)

Moreover, a comment claimed that this tests "Invalidate Region even in
case of default destructor" while in fact it tested a situaton where the
destructor is a plain declared-but-not-defined method. The invalidation
of `this` is done by the conservative evaluation, and we don't need this
overcomplicated test to validate that very basic behavior.