Create Credentials struct

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

reddit/reddit-options.go

@@ -35,17 +35,6 @@ func FromEnv(c *Client) error {
 	return nil
 }
 
-// WithCredentials sets the necessary values for the client to authenticate via OAuth2.
-func WithCredentials(id, secret, username, password string) Opt {
-	return func(c *Client) error {
-		c.ID = id
-		c.Secret = secret
-		c.Username = username
-		c.Password = password
-		return nil
-	}
-}
-
 // WithBaseURL sets the base URL for the client to make requests to.
 func WithBaseURL(u string) Opt {
 	return func(c *Client) error {