BDE test bug

[seanbaxter]

https://github.com/bloomberg/bde/blob/master/groups/bsl/bslstl/bslstl_stringview.t.cpp#L5327 (and line 5343)

I'm compiling with Circle targeting libc++. string_view.max_size() returns 18446744073709551615 on that platform, so the MAX_MAX_SIZE is (18446744073709551614) is smaller, violating the assert.