grep: remove tautological condition

st_size is an off_t, it cannot hold values larger than OFF_MAX.

CID: 1008931
(cherry picked from commit f6d6c66889001208aee7b0c46efe1c8ddffda57c)
(cherry picked from commit c816aea7abcf7a6e9471907dcb7ee3d7969a0ab3)
(cherry picked from commit b61758494286db075d5c6b68a5f2e7522e7be394)