curl: Fix cross-compilation to Windows by not forcing gssSupport

E.g. `nix build .#pkgsCross.mingwW64.curl` would fail. The params for
curl already have `gssSupport = !isStatic && …`, so removing this
doesn’t really have any effect since it’s already `true` when possible
and `false` for static platforms.

(cherry picked from commit d746f25d19)

pkgs/top-level/all-packages.nix

@@ -6706,7 +6706,6 @@ with pkgs;
     idnSupport = true;
     zstdSupport = true;
   } // lib.optionalAttrs (!stdenv.hostPlatform.isStatic) {
-    gssSupport = true;
     brotliSupport = true;
   });