refactor: remove unused MetaPluginType::None and related code

src/meta_plugin/none.rs

@@ -1,43 +0,0 @@
-use anyhow::Result;
-use log::*;
-use std::io::{self, Write};
-
-#[derive(Debug, Eq, PartialEq, Clone, Default)]
-pub struct MetaPluginNone {}
-
-impl MetaPluginNone {
-    pub fn new() -> MetaPluginNone {
-        MetaPluginNone {}
-    }
-}
-
-impl MetaPlugin for MetaPluginNone {
-    fn create(&self) -> Result<Box<dyn Write>> {
-        Ok(Box::new(DummyWriter::new()))
-    }
-
-    fn finalize(&mut self) -> io::Result<String> {
-        Ok("none".to_string())
-    }
-
-    fn update(&mut self, _data: &[u8]) {}
-}
-
-// Dummy writer that implements Write for the none meta plugin
-struct DummyWriter;
-
-impl DummyWriter {
-    fn new() -> Self {
-        DummyWriter
-    }
-}
-
-impl Write for DummyWriter {
-    fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
-        Ok(0)
-    }
-
-    fn flush(&mut self) -> io::Result<()> {
-        Ok(())
-    }
-}