Remove dependency on github.com/dgryski/go-metro

[tamird]

github.com/dgryski/go-metro is written largely in gc-syntax assembly, which makes it difficult to support gccgo downstream of it. It would be better if this library (which is used by github.com/golang/dep) did not depend on it.

cc @sdboyer

[jmank88]

go-metro is only imported by the cmd/testpaths package, which is called via go:generate from paths_test, so perhaps this can be worked around. On the other hand, its only minimally used and can likely be replaced by any old relatively uniform hash.

[tamird]

Right. Why not use the stdlib's hash/fnv?