fileshare: stop using vulnerable libmicrohttpd 0.9.70

libmicrohttpd 0.9.70 has a known criticial security issue (CVE-2021-3466)
and should be avoided.

pkgs/servers/fileshare/default.nix

···
-{ stdenv, lib, fetchgit, pkg-config, git, libmicrohttpd_0_9_70 }:
+{ stdenv, lib, fetchgit, pkg-config, git, libmicrohttpd }:
 
 stdenv.mkDerivation rec {
   pname = "fileshare";
···
   '';
 
   nativeBuildInputs = [ pkg-config git ];
-  buildInputs = [ libmicrohttpd_0_9_70 ];
+  buildInputs = [ libmicrohttpd ];
 
   makeFlags = [ "BUILD=release" ];