rubyPackages.zookeeper: drop outdated patch

Without the change build fails as:

    patch -p0 < patches/zkc-3.4.5-gcc-8.patch 2>&1
    patching file zkc-3.4.5/c/src/zookeeper.c
    Hunk #1 FAILED at 3418.
    1 out of 1 hunk FAILED -- saving rejects to file zkc-3.4.5/c/src/zookeeper.c.rej

pkgs/development/ruby-modules/gem-config/default.nix

@@ -676,11 +676,5 @@ in
 
   zookeeper = attrs: {
     buildInputs = lib.optionals stdenv.isDarwin [ cctools ];
-    dontBuild = false;
-    postPatch = ''
-      sed -i ext/extconf.rb -e "4a \
-        FileUtils.cp '${./zookeeper-ftbfs-with-gcc-8.patch}', 'patches/zkc-3.4.5-gcc-8.patch'
-      "
-    '';
   };
 }

pkgs/development/ruby-modules/gem-config/zookeeper-ftbfs-with-gcc-8.patch

@@ -1,11 +0,0 @@
---- zkc-3.4.5/c/src/zookeeper.c 2019-09-13 12:05:20.647034862 +0200
-+++ zkc-3.4.5/c/src/zookeeper.c 2019-09-13 12:05:49.125360269 +0200
-@@ -3418,7 +3418,7 @@
- 
- static const char* format_endpoint_info(const struct sockaddr_storage* ep)
- {
--    static char buf[128];
-+    static char buf[128 + 6]; // include space for the port :xxxxxx
-     char addrstr[128];
-     void *inaddr;
- #ifdef WIN32