glib: remove unnecessary substituteInPlace
glib: remove unnecessary substituteInPlace

/bin/true hasn't been hardcoded in this file since Glib 2.55.0.
2.56.0, the first stable version to include this change, was released
in 2018.

Fixes: 0973618e4ec ("gnome3: automated update")

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs