Remove the optional generic-array feature

- It can be added back later if needed
- A public dependency implies version coupling, and we can't afford to
  have it for a niche use case.

tests/generic_array.rs

@@ -1,23 +0,0 @@
-#![cfg(feature = "use_generic_array")]
-
-extern crate arrayvec;
-#[macro_use]
-extern crate generic_array;
-
-use arrayvec::ArrayVec;
-
-use generic_array::GenericArray;
-
-use generic_array::typenum::U41;
-
-#[test]
-fn test_simple() {
-    let mut vec: ArrayVec<GenericArray<i32, U41>> = ArrayVec::new();
-
-    assert_eq!(vec.len(), 0);
-    assert_eq!(vec.capacity(), 41);
-    vec.extend(0..20);
-    assert_eq!(vec.len(), 20);
-    assert_eq!(&vec[..5], &[0, 1, 2, 3, 4]);
-}
-