Remove default comparison for binary search

Remove default comparison for binary search

clang++ complains about this, and we never rely on the default
comparison in our code.

/home/gperciva/src/lilypond/flower/include/std-vector.hh:197:36:
error: 'T' does
      not refer to a value
               Compare less = less<T> (),
                                   ^
/home/gperciva/src/lilypond/flower/include/std-vector.hh:193:19:
note: declared
      here
template<typename T, typename Compare>
                  ^
/home/gperciva/src/lilypond/flower/include/std-vector.hh:197:40:
error:
      expected expression
               Compare less = less<T> (),