Removed the reset of mode_info from previous frame

Prior to this commit, both encoder and decoder reset mode/mv info from
previous frame in error resilient mode to ensure bitstreams are able to
decode when there is loss of frame in decoder side. However, this is
not necessary. This commit changed to remove the reset, so encoder can
continue to use mode/mv/partition information from previously encoded
frame without affecting decodeablilty under loss of frame.

Change-Id: I0279f862900dc647fb471ae3389770bb1b9f454f