TST/CI: speed up chunksize test
Seeing lots of CI timeouts - this test sometimes takes > 5 min for the python parser, guessing dependent on memory availability. 

AFAICT the data size is only so large to test the warning given by the c parser and low memory case, so shrank size for other cases.
Also tentatively removed resource warning handling as hoping that was only needed because of memory issues. thanks @mzeitlin11  @meeseeksdev backport 1.3.x Something went wrong ... Please have  a look at my logs.