Remove redundant includes from MallctlHelperTest.cpp

Summary:
Remove 3 unused include directives from `fbcode/folly/memory/test/MallctlHelperTest.cpp`:

- `folly/CPortability.h` - transitively included via `MallctlHelper.h → Malloc.h → Portability.h → CPortability.h`
- `folly/memory/Malloc.h` - transitively included via `MallctlHelper.h → Malloc.h`
- `folly/portability/SysTypes.h` - `ssize_t` available transitively through other included system headers

Reviewed By: dmm-fb

Differential Revision: D95404412

fbshipit-source-id: 96a55ee87f7bc7345d39436e581a49fea5df2c1c

Author: yfeldblum

third-party/folly/src/folly/memory/test/MallctlHelperTest.cpp

@@ -16,10 +16,7 @@
 
 #include <folly/memory/MallctlHelper.h>
 
-#include <folly/CPortability.h>
-#include <folly/memory/Malloc.h>
 #include <folly/portability/GTest.h>
-#include <folly/portability/SysTypes.h>
 
 #if defined(FOLLY_USE_JEMALLOC) && (!defined(FOLLY_SANITIZE) || !FOLLY_SANITIZE)
 #include <jemalloc/jemalloc.h>