Revert "sanitizer_common: optimize memory drain"
This reverts commit
072669521456a369409cf9db30739a3fac740173.
This causes the following build failure with gcc 10.3.0:
/home/nikic/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h:114:31: error: declaration of ‘typedef class __sanitizer::MemoryMapper<__sanitizer::SizeClassAllocator64<Params> > __sanitizer::SizeClassAllocator64<Params>::MemoryMapper’ changes meaning of ‘MemoryMapper’ [-fpermissive]
114 | typedef MemoryMapper<ThisT> MemoryMapper;