Remove uses of option_filter feature

Author: tmccombs

src/libcore/option.rs

@@ -628,8 +628,6 @@ impl<T> Option<T> {
     /// # Examples
     ///
     /// ```rust
-    /// #![feature(option_filter)]
-    ///
     /// fn is_even(n: &i32) -> bool {
     ///     n % 2 == 0
     /// }

src/librustc_typeck/lib.rs

@@ -81,7 +81,6 @@ This API is completely unstable and subject to change.
 #![feature(from_ref)]
 #![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(exhaustive_patterns)]
-#![feature(option_filter)]
 #![feature(quote)]
 #![feature(refcell_replace_swap)]
 #![feature(rustc_diagnostic_macros)]