cut out-of-line definition for constexpr static data member in to_asc…

…ii bench

Summary:
Mitigates this warning:
```
folly\lang\test\ToAsciiBench.cpp(116): warning C5041: 'data': out-of-line definition for constexpr static data member is not needed and is deprecated in C++17
folly\lang\test\ToAsciiBench.cpp(140): warning C5041: 'data': out-of-line definition for constexpr static data member is not needed and is deprecated in C++17
```

Reviewed By: ispeters

Differential Revision: D67657368

fbshipit-source-id: d31d2566c1cdfc80cfd79e08dac0c9ce2aa9eed3

folly/lang/test/ToAsciiBench.cpp

@@ -113,7 +113,6 @@ struct inputs<10> {
       12345678901234567890u,
   };
 };
-constexpr uint64_t const inputs<10>::data[21];
 
 template <>
 struct inputs<16> {
@@ -137,7 +136,6 @@ struct inputs<16> {
       0x123456789abcdef0,
   };
 };
-constexpr uint64_t const inputs<16>::data[17];
 
 } // namespace