configure: Remove --enable-rw-rootfs detect using /etc/fstab instead

This patch removes the --enable-rw-rootfs build flag.  Like OpenRC we
now check /etc/fstab instad; if `/` is listed *and* doesn't have the
`ro` flag set, we remount / read-write.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

contrib/void/build.sh

@@ -14,7 +14,7 @@ fi
 # The plugins are optional, but you may need D-Bus and X11 if you want
 # to run X-Window, the other configure flags are however required.
 PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig:/usr/local/lib/pkgconfig ./configure	\
-		 --enable-rw-rootfs            --enable-progress		\
+		                               --enable-progress		\
                  --enable-dbus-plugin          --enable-x11-common-plugin	\
 		 --enable-alsa-utils-plugin    --enable-inetd-echo-plugin	\
 		 --enable-inetd-chargen-plugin --enable-inetd-daytime-plugin	\