We no longer allow out < in in-place operations

The (rather long...) preamble to aead.h still said we allowed this.

Change-Id: I4ba02ef196c6d5439408000cf3c296111b55ff36
Reviewed-on: https://boringssl-review.googlesource.com/11004
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/include/openssl/aead.h b/include/openssl/aead.h
index 71071d2..0cad405 100644
--- a/include/openssl/aead.h
+++ b/include/openssl/aead.h
@@ -82,10 +82,8 @@
  * permits implicit context to be authenticated but may be empty if not needed.
  * The "seal" and "open" operations may work in-place if the |out| and |in|
- * arguments are equal. They may also be used to shift the data left inside the
- * same buffer if |out| is less than |in|. However, |out| may not point inside
- * the input data otherwise the input may be overwritten before it has been
- * read. This situation will cause an error.
+ * arguments are equal. Otherwise, if |out| and |in| alias, input data may be
+ * overwritten before it is read. This situation will cause an error.
  * The "seal" and "open" operations return one on success and zero on error. */