qemu-sockets: do not test path with access() before unlinking

Using access() is a time-of-check/time-of-use race condition.  It is
okay to use them to provide better error messages, but that is pretty
much it.

This is not one such case; on the other hand, access() *will* skip
unlink() for a non-existent path, so ignore ENOENT return values from
the unlink() system call.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
