Remove unused Output implementations

I think the OutputStream was used only in old fish_indent code.
The BufferedOutputter seems obsolete, maybe because DerefMut covers
this.

src/io.rs

@@ -11,7 +11,6 @@
 use crate::proc::JobGroupRef;
 use crate::redirection::{RedirectionMode, RedirectionSpecList};
 use crate::signal::SigChecker;
-use crate::terminal::Output;
 use crate::topic_monitor::Topic;
 use crate::wutil::{perror, perror_io, unescape_bytes_and_write_to_fd, wdirname, wstat};
 use errno::Errno;
@@ -732,13 +731,6 @@ pub fn append_narrow_buffer(&mut self, buffer: &SeparatedBuffer) -> bool {
     }
 }
 
-impl Output for OutputStream {
-    fn write_bytes(&mut self, command_part: &[u8]) {
-        // TODO Retry on interrupt.
-        self.append(&bytes2wcstring(command_part));
-    }
-}
-
 /// An output stream for builtins which outputs to an fd.
 /// Note the fd may be something like stdout; there is no ownership implied here.
 pub struct FdOutputStream {

src/terminal.rs

@@ -755,12 +755,6 @@ fn deref_mut(&mut self) -> &mut Self::Target {
     }
 }
 
-impl<'a> Output for BufferedOutputter<'a> {
-    fn write_bytes(&mut self, buf: &[u8]) {
-        self.0.write_bytes(buf);
-    }
-}
-
 /// Given a list of RgbColor, pick the "best" one, as determined by the color support. Returns
 /// RgbColor::NONE if empty.
 pub fn best_color(candidates: impl Iterator<Item = Color>, support: ColorSupport) -> Option<Color> {