build: remove unused install.sh (#7124)

install.sh was used for AC_PROG_INSTALL, which was removed in
4421517c55 (corresponding PR #5133)

From the manual of GNU Autoconf (version 2.73):

>     Autoconf comes with a copy of ‘install-sh’ that you can use.  If
>     you use ‘AC_PROG_INSTALL’, you must include ‘install-sh’ in your
>     distribution; otherwise ‘autoreconf’ and ‘configure’ will produce
>     an error message saying they can’t find it—even if the system
>     you’re on has a good ‘install’ program.  This check is a safety
>     measure to prevent you from accidentally leaving that file out,
>     which would prevent your package from installing on systems that
>     don’t have a BSD-compatible ‘install’ program.

If install-sh wasn't found, configure would check for install.sh in
srcdir. install.sh is a placeholder that does nothing, without it
configure would abort.

.github/workflows/build.yml

@@ -26,7 +26,6 @@ on:
       - config.sh.in
       - configure
       - configure.ac
-      - install.sh
       - mkdeb.sh
       - mketc.sh
   pull_request:
@@ -47,7 +46,6 @@ on:
       - config.sh.in
       - configure
       - configure.ac
-      - install.sh
       - mkdeb.sh
       - mketc.sh
 

Makefile

@@ -325,7 +325,6 @@ DISTFILES = \
 	configure.ac \
 	contrib \
 	etc \
-	install.sh \
 	m4 \
 	mkdeb.sh \
 	mketc.sh \

install.sh

@@ -1,6 +0,0 @@
-#!/bin/sh
-# This file is part of Firejail project
-# Copyright (C) 2014-2026 Firejail Authors
-# License GPL v2
-
-echo "installing..."