classes/cargo: don't override PATCHTOOL

The referenced issue is fixed upstream

Signed-off-by: Tyler Hall <tylerwhall@gmail.com>

classes/cargo.bbclass

@@ -11,10 +11,6 @@ def cargo_base_dep(d):
 
 BASEDEPENDS_append = " ${@cargo_base_dep(d)}"
 
-# FIXME: this is a workaround for a misbehavior in cargo when used with quilt.
-# See https://github.com/rust-lang/cargo/issues/978
-PATCHTOOL = "patch"
-
 # Cargo only supports in-tree builds at the moment
 B = "${S}"