remove frivolous mime guessing dep

src/agent.rs

@@ -332,18 +332,6 @@ fn basic_auth(user: &str, pass: &str) -> String {
     ::base64::encode(&format!("{}:{}", safe, pass))
 }
 
-fn mime_of<S: Into<String>>(s: S) -> String {
-    let s = s.into();
-    match &s[..] {
-        "json" => "application/json",
-        "form" => "application/x-www-form-urlencoded",
-        _ => match ::mime_guess::get_mime_type_str(&s) {
-            Some(mime) => mime,
-            None => "foo",
-        },
-    }.to_string()
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;