msm: mdss: remove HDMI connected flags

There's no need to check whether the device has been connected
when disconnect it, for we'll always do disconnect after the device
has been connected. Even if we do disconnect incorrectly, it'll not
affect. Now we have both ASYNC_AUDIO/VIDEO flag and SYNC_AUDIO/
VIDEO flag. Sometimes SYNC flag would be set when device is connected,
while ASYNC flag is set when disconnect, the two flags are not match.
If we check here, that would return false. So we could remove the flags.

CRs-Fixed: 2033810
Change-Id: I305f64352815cd38a4c9618bcd22a4d103c14818
Signed-off-by: zhaoyuan <yzhao@codeaurora.org>