Revert "vp9_ethread: include a pointer to mb in VP9_COMP"

This reverts commit 6906d218ddd1af97228a797f4558e402231d94f1.

Another way will be used to handle mb struct.

Change-Id: Ic1111a46b2b1ee00f8f9e3fcd4cf3eb6030b2dc4
vp9_ethread: change mask_filter to a local variable

The mask_filter in RD_OPT struct is used to record rd result in
filter decision. It is only used in pick_inter_mode functions,
and is removed from the struct and declared as a local variable.

Change-Id: I3c95c8632ba7241591ce00ef2ef5677b5e297d7b
Merge "Revert "vp9_ethread: include a pointer to mb in VP9_COMP""
Merge "vp9_ethread: change mask_filter to a local variable"