[lldb/test] Remove a check from TestLoadAfterAttach

The two module retrieval methods (qXfer:libraries-svr4 and manual list
traversal) differ in how the handle the
manually-added-but-not-yet-loaded modules. The svr4 path will remove it,
while the manual one will keep in the list.

It's likely the two paths need ought to be synchronized, but right now,
this distinction is not relevant for the test.