setenv: Simplify m4 requires

[Bruno Haible]

lib/setenv.c does not reference HAVE_ALLOCA any more since 2004-01-20.
It uses the 'malloca' module now.


2023-06-19  Bruno Haible  <bruno@clisp.org>

        setenv: Simplify m4 requires.
        * m4/setenv.m4 (gl_PREREQ_SETENV): Don't require AC_FUNC_ALLOCA.

diff --git a/m4/setenv.m4 b/m4/setenv.m4
index ef068ad879..a30523d6a3 100644
--- a/m4/setenv.m4
+++ b/m4/setenv.m4
@@ -1,4 +1,4 @@
-# setenv.m4 serial 32
+# setenv.m4 serial 33
 dnl Copyright (C) 2001-2004, 2006-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -151,7 +151,6 @@ AC_DEFUN([gl_FUNC_UNSETENV]
 # Prerequisites of lib/setenv.c.
 AC_DEFUN([gl_PREREQ_SETENV],
 [
-  AC_REQUIRE([AC_FUNC_ALLOCA])
   AC_REQUIRE([gl_ENVIRON])
   AC_CHECK_HEADERS_ONCE([unistd.h])
   AC_CHECK_HEADERS([search.h])