Partially revert #107200

`Ok(0)` is indeed something the caller may interpret as an error, but
that's the *correct* thing to return if the writer can't accept any more
bytes.

Author: joshtriplett

library/std/src/io/mod.rs

@@ -1425,9 +1425,9 @@ pub trait Write {
     ///
     /// If this method consumed `n > 0` bytes of `buf` it must return [`Ok(n)`].
     /// If the return value is `Ok(n)` then `n` must satisfy `n <= buf.len()`.
-    /// Unless `buf` is empty, this function shouldn’t return `Ok(0)` since the
-    /// caller may interpret that as an error.  To indicate lack of space,
-    /// implementors should return [`ErrorKind::StorageFull`] error instead.
+    /// A return value of `Ok(0)` typically means that the underlying object is
+    /// no longer able to accept bytes and will likely not be able to in the
+    /// future as well, or that the buffer provided is empty.
     ///
     /// # Errors
     ///