Revert "pkgsMusl.socat: fix build"

This reverts commit 7ecf7a3493.

This is no longer necessary as of socat 1.7.4.4, and in fact breaks
the build.

Fixes: 497c7f26aa ("socat: 1.7.4.3 -> 1.7.4.4")

pkgs/tools/networking/socat/default.nix

@@ -23,11 +23,6 @@ stdenv.mkDerivation rec {
       --replace /sbin/ifconfig ifconfig
   '';
 
-  configureFlags = lib.optionals stdenv.hostPlatform.isMusl [
-    # musl doesn't have getprotobynumber_r
-    "sc_cv_getprotobynumber_r=2"
-  ];
-
   buildInputs = [ openssl readline ];
 
   hardeningEnable = [ "pie" ];