meson.build: drop suggest-attribute=noreturn build option

meson.build: drop suggest-attribute=noreturn build option

The suggest-attribute=noreturn option marks functions which will
never return, to give the compiler some hints.  It catches all of
our src/lxc/tools/*.c *_main functions as follows:

error: function might be candidate for attribute ‘noreturn’ [-Werror=suggest-attribute=noreturn]

But if we mark those __noreturn, then  the compiler complains that:

../src/lxc/tools/lxc_attach.c:320:53: warning: ‘main’ specifies less restrictive attribute than its target ‘lxc_attach_main’: ‘noreturn’ [-Wmissi
ng-attributes]
  320 | int __attribute__((weak, alias("lxc_attach_main"))) main(int argc, char *argv[]);

This recommendation is really not very important, so let's not ask
the build to warn about it.

Signed-off-by: Serge Hallyn <serge@hallyn.com>