mesa: fix build on Darwin

Mesa 26.1.4 includes commit[1] which makes installed Gallium
driver names use libname_suffix. Remove obsolete workaround.

[1]: https://gitlab.freedesktop.org/mesa/mesa/-/commit/ad9e702a79e6c4603004eb0fe378abac4274777d

pkgs/development/libraries/mesa/darwin.nix

@@ -59,13 +59,6 @@ stdenv.mkDerivation {
     ./opencl.patch
   ];
 
-  postPatch = ''
-    # Darwin only installs `swrast_dri.so`. It is symlinked to `libdril_dri.dylib`, but the script never terminates
-    # checking for `swrast_dri.dylib`, which isn’t what will be created.
-    substituteInPlace bin/install_megadrivers.py \
-      --replace-fail "            while ext != '.' + args.libname_suffix" "            while ext != '.so'"
-  '';
-
   outputs = [
     "out"
     "dev"