init.qcom.rc: Remove /data/system/wpa_supplicant, fixes WiFi on upgrades

libhardware_legacy's wifi_connect_to_supplicant checks if (the symlink)
/data/system/wpa_supplicant exists, and if so, assumes it points to a
directory containing the wpa_supplicant control socket.  This is _not_ the
location of the wpa_supplicant control socket on d2/jf, and so, the symlink
should not exist.

CM 10.2's init.qcom.rc creates the /data/system/wpa_supplicant symlink,
with /data/misc/wifi/wpa_supplicant as its target.  However, it does not
create the target directory itself, so the wifi_connect_to_supplicant check
(correctly) fails.

CM 11.0 does create the /data/misc/wifi/wpa_supplicant directory, but not
the corresponding /data/system/wpa_supplicant symlink.  So the
wifi_connect_to_supplicant check also fails.  However, as the symlink
already exists on 10.2 upgrades, the check passes, resulting in
wpa_supplicant attempting to use the non-existant
/data/system/wpa_supplicant/wlan0 control socket.  Thus, the
/data/system/wpa_supplicant symlink needs to be removed to ensure that WiFi
on upgrade installs functions corectly.

Change-Id: Ifd49fa31706f9c09594eb8c45a726f0e6abef252