Remove replace directives and use own fork to make go get work again (#1028)

See https://github.com/golang/go/issues/30354
go get doesn't honor the go.mod replace options.

vendor/github.com/bwmarrin/discordgo/user.go

@@ -1,69 +0,0 @@
-package discordgo
-
-import "strings"
-
-// A User stores all data for an individual Discord user.
-type User struct {
-	// The ID of the user.
-	ID string `json:"id"`
-
-	// The email of the user. This is only present when
-	// the application possesses the email scope for the user.
-	Email string `json:"email"`
-
-	// The user's username.
-	Username string `json:"username"`
-
-	// The hash of the user's avatar. Use Session.UserAvatar
-	// to retrieve the avatar itself.
-	Avatar string `json:"avatar"`
-
-	// The user's chosen language option.
-	Locale string `json:"locale"`
-
-	// The discriminator of the user (4 numbers after name).
-	Discriminator string `json:"discriminator"`
-
-	// The token of the user. This is only present for
-	// the user represented by the current session.
-	Token string `json:"token"`
-
-	// Whether the user's email is verified.
-	Verified bool `json:"verified"`
-
-	// Whether the user has multi-factor authentication enabled.
-	MFAEnabled bool `json:"mfa_enabled"`
-
-	// Whether the user is a bot.
-	Bot bool `json:"bot"`
-}
-
-// String returns a unique identifier of the form username#discriminator
-func (u *User) String() string {
-	return u.Username + "#" + u.Discriminator
-}
-
-// Mention return a string which mentions the user
-func (u *User) Mention() string {
-	return "<@" + u.ID + ">"
-}
-
-// AvatarURL returns a URL to the user's avatar.
-//    size:    The size of the user's avatar as a power of two
-//             if size is an empty string, no size parameter will
-//             be added to the URL.
-func (u *User) AvatarURL(size string) string {
-	var URL string
-	if u.Avatar == "" {
-		URL = EndpointDefaultUserAvatar(u.Discriminator)
-	} else if strings.HasPrefix(u.Avatar, "a_") {
-		URL = EndpointUserAvatarAnimated(u.ID, u.Avatar)
-	} else {
-		URL = EndpointUserAvatar(u.ID, u.Avatar)
-	}
-
-	if size != "" {
-		return URL + "?size=" + size
-	}
-	return URL
-}