removed the contains feature from library/core/Cargo.toml

Author: yonikremer

library/core/Cargo.toml

@@ -36,8 +36,6 @@ optimize_for_size = []
 # Make `RefCell` store additional debugging information, which is printed out when
 # a borrow error occurs
 debug_refcell = []
-# Adds a function to check if an element is contained in an iterator
-contains = []
 
 [lints.rust.unexpected_cfgs]
 level = "warn"