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

Fixes:

```
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:131: warning: unused parameter ‘text’ [-Wunused-parameter]
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:131: warning: unused parameter ‘file’ [-Wunused-parameter]
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:131: warning: unused parameter ‘line’ [-Wunused-parameter]
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp: In function ‘int main(int, char**)’:
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:847: warning: unused variable ‘constContainer’ [-Wunused-variable]
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:916: warning: comparison between signed and unsigned integer expressions
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:372: warning: unused variable ‘veryVeryVerbose’ [-Wunused-variable]
../groups/bsl/bslstl/bslstl_forwarditerator.t.cpp:373: warning: unused variable ‘veryVeryVeryVerbose’ [-Wunused-variable]
```