Use patch not feature to fix rustdoc build.

aosp/1797429 enabled a new feature to fix the rustdoc build.  This
removes that feature and instead uses a patch (which has already been
merged upstream) to fix the issue.

Test: m rustdoc
Change-Id: I2f0088625304ae4bf9fc349e0a64fe0bcf5a4c21
diff --git a/src/traits.rs b/src/traits.rs
index bd4d070..aae96e5 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -5,7 +5,18 @@
 ///
 /// The returned object uses zero-copy, and so has the same lifetime as the input.
 ///
-/// Note that only parsing is done, not validation (see the [`Validate`](crate::validate::Validate) trait).
+#[cfg_attr(
+    feature = "validate",
+    doc = r#"
+Note that only parsing is done, not validation (see the [`Validate`](crate::validate::Validate) trait).
+"#
+)]
+#[cfg_attr(
+    not(feature = "validate"),
+    doc = r#"
+Note that only parsing is done, not validation.
+"#
+)]
 ///
 /// # Example
 ///