[lldb][test] Consolidate generic and libcxx std::deque formatter tests (#146697)
The plan is to move all STL formatter API tests into a single directory.
The `std::deque` test is currently the only test that is duplicated
between the `libcxx` and `generic` directories. This patch moves the
libcxx deque tests into `generic` (moving over any functionality that
wasn't tested in the `generic` tests, mainly formatting
pointers/references to `std::deque`).