Auto merge of #4714 - msizanoen1:remove-plugin, r=Manishearth

Remove clippy plugin

This PR removes the clippy plugin, which is already deprecated and is causing the `fmt_macros` not found error in rust-lang/rust#62558: https://github.com/rust-lang/rust/issues/62558#issuecomment-529884322

changelog: remove plugin interface

Cargo.toml

@@ -22,11 +22,6 @@ publish = false
 travis-ci = { repository = "rust-lang/rust-clippy" }
 appveyor = { repository = "rust-lang/rust-clippy" }
 
-[lib]
-name = "clippy"
-plugin = true
-test = false
-
 [[bin]]
 name = "cargo-clippy"
 test = false

src/lib.rs

@@ -1,35 +0,0 @@
-// error-pattern:cargo-clippy
-#![feature(plugin_registrar)]
-#![feature(rustc_private)]
-#![warn(rust_2018_idioms)]
-
-// FIXME: switch to something more ergonomic here, once available.
-// (Currently there is no way to opt into sysroot crates without `extern crate`.)
-#[allow(unused_extern_crates)]
-extern crate rustc_driver;
-use self::rustc_driver::plugin::Registry;
-
-#[plugin_registrar]
-pub fn plugin_registrar(reg: &mut Registry<'_>) {
-    for (lint, _, _) in reg.lint_store.get_lint_groups() {
-        reg.sess
-            .struct_warn(
-                "the clippy plugin is being deprecated, please use cargo clippy or rls with the clippy feature",
-            )
-            .emit();
-        if lint == "clippy" {
-            // cargo clippy run on a crate that also uses the plugin
-            return;
-        }
-    }
-
-    let conf = clippy_lints::read_conf(reg.args(), &reg.sess);
-    clippy_lints::register_plugins(&mut reg.lint_store, &reg.sess, &conf);
-}
-
-// only exists to let the dogfood integration test works.
-// Don't run clippy as an executable directly
-#[allow(dead_code)]
-fn main() {
-    panic!("Please use the cargo-clippy executable");
-}