bslstl_bidirectionaliterator.t: Fix unused, signed/unsigned warnings.

Fixes:

```
../groups/bsl/bslstl/bslstl_bidirectionaliterator.t.cpp: In function ‘int main(int, char**)’:
../groups/bsl/bslstl/bslstl_bidirectionaliterator.t.cpp:1217: warning: unused variable ‘constContainer’ [-Wunused-variable]
../groups/bsl/bslstl/bslstl_bidirectionaliterator.t.cpp:1287: warning: comparison between signed and unsigned integer expressions
../groups/bsl/bslstl/bslstl_bidirectionaliterator.t.cpp:637: warning: unused variable ‘veryVeryVerbose’ [-Wunused-variable]
../groups/bsl/bslstl/bslstl_bidirectionaliterator.t.cpp:638: warning: unused variable ‘veryVeryVeryVerbose’ [-Wunused-variable]
```