Fix compilation on latest nightly

The ability for plugins to add MIR passes was removed as of 4ca9c97.
Luckily, we don't use this feature at all and can safely ignore it.

Fixes rust-lang#1618

Author: Techcable

src/main.rs

@@ -89,7 +89,6 @@ impl<'a> CompilerCalls<'a> for ClippyCompilerCalls {
                                                            lint_groups,
                                                            llvm_passes,
                                                            attributes,
-                                                           mir_passes,
                                                            .. } = registry;
                     let sess = &state.session;
                     let mut ls = sess.lint_store.borrow_mut();
@@ -105,7 +104,6 @@ impl<'a> CompilerCalls<'a> for ClippyCompilerCalls {
                     }
 
                     sess.plugin_llvm_passes.borrow_mut().extend(llvm_passes);
-                    sess.mir_passes.borrow_mut().extend(mir_passes);
                     sess.plugin_attributes.borrow_mut().extend(attributes);
                 }
                 old(state);