v4l2_codec2: Cleanup unused includes.

This CL cleans up a few unused includes in the encode helpers.

Bug: 155138142
Test: arc.VideoEncodeAccel.h264_192p_i420_vm
Change-Id: I41edd1d95b92410d8bb143ebb2d2da26eef0c01e

common/EncodeHelpers.cpp

@@ -8,7 +8,6 @@
 #include <v4l2_codec2/common/EncodeHelpers.h>
 
 #include <linux/v4l2-controls.h>
-#include <string.h>
 
 #include <C2AllocatorGralloc.h>
 #include <cutils/native_handle.h>

common/include/v4l2_codec2/common/EncodeHelpers.h

@@ -6,7 +6,6 @@
 #define ANDROID_V4L2_CODEC2_COMMON_HELPERS_H
 
 #include <C2Config.h>
-#include <C2ParamDef.h>
 #include <system/graphics.h>
 
 #include <size.h>