Remove 'ALIGNAS' from StatisticsImpl. (#4061)

Summary:
Remove over-alignment on `StatisticsImpl` whose benefit is vague and causes UBSAN check to fail due to `std::make_shared` not respecting the over-alignment requirement.

Test plan
```
$ make clean && COMPILE_WITH_UBSAN=1 OPT=-g make -j16 ubsan_check
```
Closes https://github.com/facebook/rocksdb/pull/4061

Differential Revision: D8656506

Pulled By: riversand963

fbshipit-source-id: db355ae9c7bdd2c9e9c5e63cabba13d8d82cc5f9

monitoring/statistics.h

@@ -40,7 +40,7 @@ enum HistogramsInternal : uint32_t {
 };
 
 
-class ALIGN_AS(CACHE_LINE_SIZE) StatisticsImpl : public Statistics {
+class StatisticsImpl : public Statistics {
  public:
   StatisticsImpl(std::shared_ptr<Statistics> stats,
                  bool enable_internal_stats);