Delete fstab.script from SL-Micro test build

This was only needed when /var was an extra partition, but
it's a volume with copy-on-write disabled for some time

build-tests/x86/tumbleweed/test-image-MicroOS/root/etc/fstab.script

@@ -1,9 +0,0 @@
-#!/bin/sh
-set -eux
-
-/usr/sbin/setup-fstab-for-overlayfs
-# If /var is on a different partition than /...
-if [ "$(findmnt -snT / -o SOURCE)" != "$(findmnt -snT /var -o SOURCE)" ]; then
-    # ... set options for autoexpanding /var
-    gawk -i inplace '$2 == "/var" { $4 = $4",x-growpart.grow,x-systemd.growfs" } { print $0 }' /etc/fstab
-fi