Removed unused vendored dependencies (#6520)

vendor/github.com/lib/pq/user_posix.go

@@ -1,24 +0,0 @@
-// Package pq is a pure Go Postgres driver for the database/sql package.
-
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris rumprun
-
-package pq
-
-import (
-	"os"
-	"os/user"
-)
-
-func userCurrent() (string, error) {
-	u, err := user.Current()
-	if err == nil {
-		return u.Username, nil
-	}
-
-	name := os.Getenv("USER")
-	if name != "" {
-		return name, nil
-	}
-
-	return "", ErrCouldNotDetectUsername
-}