avoid triggering gcc's -Wunsafe-loop-optimizations in EDSP

avoid triggering gcc's -Wunsafe-loop-optimizations in EDSP

apt/apt-pkg/edsp.cc: In function ‘bool EDSP::WriteLimitedScenario(pkgDepCache&, FILE*, const PackageSet&, OpProgress*)’:
apt/apt-pkg/edsp.cc:245:56: warning: cannot optimize loop, the loop counter may overflow [-Wunsafe-loop-optimizations]
    std::string dependencies[pkgCache::Dep::Enhances + 1];
                                                        ^
Using a std::array to silence gcc as well as as a code improvement feels right here.

Git-Dch: Ignore