kent: enable patches if needed.

This is required by BioBigFile, which needs an older Kent version.

pkgs/applications/science/biology/kent/default.nix

@@ -24,16 +24,12 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ libpng libuuid zlib bzip2 xz openssl curl libmysqlclient ];
 
-  patchPhase = ''
-    runHook prePatch
-
+  postPatch = ''
     substituteInPlace ./src/checkUmask.sh \
       --replace "/bin/bash" "${bash}/bin/bash"
 
     substituteInPlace ./src/hg/sqlEnvTest.sh \
       --replace "which mysql_config" "${which}/bin/which ${libmysqlclient}/bin/mysql_config"
-
-    runHook postPatch
   '';
 
   buildPhase = ''