Fix bslstl::shared_ptr build in -std=c++11 due to typo.

Somehow a spurious semi-colon wound up in the header definition of one of the functions. Caused compilation error in `-std=c++11` mode:

```
bde/groups/bsl/bslstl/bslstl_sharedptr.h:4965:1: error: expected unqualified-id
{
^
```