autotools: remove FORCE_UNSAFE_CONFIGURE from docs, commands, code (#16145)

Since #16132, we've consolidated the setting of FORCE_UNSAFE_CONFIGURE to
`autotools.py`, so we don't need to use it in packages like `coreutils`,
in our commands, or in our container recipes.

- [x] Remove FORCE_UNSAFE_CONFIGURE from packages
- [x] Remove FORCE_UNSAFE_CONFIGURE from container recipes
- [x] Remove FORCE_UNSAFE_CONFIGURE from `spack ci` command

var/spack/repos/builtin/packages/coreutils/package.py

@@ -34,6 +34,5 @@ def configure_args(self):
                 configure_args.append('--program-prefix=g')
             configure_args.append('--without-gmp')
             configure_args.append('gl_cv_func_ftello_works=yes')
-            configure_args.append('FORCE_UNSAFE_CONFIGURE=1')
 
             return configure_args