chore: rebrand Nix to Lix when it makes sense

Here's my guide so far:

$ rg '((?!(recursive).*) Nix
(?!(daemon|store|expression|Rocks!|Packages|language|derivation|archive|account|user|sandbox|flake).*))'
-g '!doc/' --pcre2

All items from this query have been tackled. For the documentation side:
that's for https://git.lix.systems/lix-project/lix/issues/162.

Additionally, all remaining references to github.com/NixOS/nix which
were not relevant were also replaced.

Fixes: https://git.lix.systems/lix-project/lix/issues/148.
Fixes: https://git.lix.systems/lix-project/lix/issues/162.
Change-Id: Ib3451fae5cb8ab8cd9ac9e4e4551284ee6794545
Signed-off-by: Raito Bezarius <raito@lix.systems>

perl/configure.ac

@@ -29,7 +29,7 @@ NEED_PROG(xz, xz)
 AC_MSG_CHECKING([whether Perl is recent enough])
 if ! $perl -e 'open(FOO, "-|", "true"); while (<FOO>) { print; }; close FOO or die;'; then
     AC_MSG_RESULT(no)
-    AC_MSG_ERROR([Your Perl version is too old.  Nix requires Perl 5.8.0 or newer.])
+    AC_MSG_ERROR([Your Perl version is too old.  Lix requires Perl 5.8.0 or newer.])
 fi
 AC_MSG_RESULT(yes)