Use more impl header lifetime elision

There are two big categories of changes in here

- Removing lifetimes from common traits that can essentially never user a lifetime from an input (particularly `Drop` & `Debug`)
- Forwarding impls that are only possible because the lifetime doesn't matter (like `impl<R: Read + ?Sized> Read for &mut R`)

I omitted things that seemed like they could be more controversial, like the handful of iterators that have a `Item: 'static` despite the iterator having a lifetime or the `PartialEq` implementations where the flipped one cannot elide the lifetime.

src/libstd/panic.rs

@@ -199,9 +199,9 @@ pub struct AssertUnwindSafe<T>(
 // * Our custom AssertUnwindSafe wrapper is indeed unwind safe
 
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-impl<'a, T: ?Sized> !UnwindSafe for &'a mut T {}
+impl<T: ?Sized> !UnwindSafe for &mut T {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-impl<'a, T: RefUnwindSafe + ?Sized> UnwindSafe for &'a T {}
+impl<T: RefUnwindSafe + ?Sized> UnwindSafe for &T {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T: RefUnwindSafe + ?Sized> UnwindSafe for *const T {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
@@ -320,7 +320,7 @@ impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> {
 }
 
 #[unstable(feature = "futures_api", issue = "50547")]
-impl<'a, F: Future> Future for AssertUnwindSafe<F> {
+impl<F: Future> Future for AssertUnwindSafe<F> {
     type Output = F::Output;
 
     fn poll(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {