Delete from table rows where any of the column field is null
I see two ways of doing that:

With plain standard SQL, simply list all columns and combine that with an OR:

delete from the_table
where date is null
   or persons is null
   or two_wheelers is null
   or cars is null
   or vans is null
   or buses is null
   or autos is null;


Another (Postgres specific) solution is the comparison of the whole row with NOT NULL

select *
from the_table
where the_table is not null;


will return only rows where all columns are not null. You want the opposite, so you need to negate that where not (the_table is not null) The condition where the_table is null is something different - that only matches rows where all columns are null. 

delete from the_table
where not (the_table is not null);