[plugins] Remove unneeded .mli files

src/plugins/aorai/tests/Aorai_test.mli

-(* Nothing is exported. *)

src/plugins/aorai/tests/ya/name_projects.mli

-(* nothing is exported. *)

src/plugins/e-acsl/tests/print.mli

-(**************************************************************************)
-(*                                                                        *)
-(*  This file is part of the Frama-C's E-ACSL plug-in.                    *)
-(*                                                                        *)
-(*  Copyright (C) 2012-2020                                               *)
-(*    CEA (Commissariat à l'énergie atomique et aux énergies              *)
-(*         alternatives)                                                  *)
-(*                                                                        *)
-(*  you can redistribute it and/or modify it under the terms of the GNU   *)
-(*  Lesser General Public License as published by the Free Software       *)
-(*  Foundation, version 2.1.                                              *)
-(*                                                                        *)
-(*  It is distributed in the hope that it will be useful,                 *)
-(*  but WITHOUT ANY WARRANTY; without even the implied warranty of        *)
-(*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *)
-(*  GNU Lesser General Public License for more details.                   *)
-(*                                                                        *)
-(*  See the GNU Lesser General Public License version 2.1                 *)
-(*  for more details (enclosed in the file licenses/LGPLv2.1).            *)
-(*                                                                        *)
-(**************************************************************************)