[zip] Stop calculating crc if it's not checked

Crc calculation shows up in the profiler in 2-5% range, and is
never currently validated. Let's disable it for good.
For a well-compressible test data the difference is even nicer:

Benchmark                       Time          CPU        Iteration
------------------------------------------------------------------
ziparchive-benchmarks:
before:
  #ExtractEntry/2            1943244 ns    1926758 ns          375
  #ExtractEntry/16           1877295 ns    1867049 ns          375
  #ExtractEntry/1024         1888772 ns    1879976 ns          373
after:
  #ExtractEntry/2             817003 ns     812870 ns          874
  #ExtractEntry/16            814029 ns     809813 ns          875
  #ExtractEntry/1024          804904 ns     800972 ns          879

Bug: 153392568
Test: atest, manual
Change-Id: I917abecab01301f1d09a5bf3b542d24b3875e359
Merged-In: I917abecab01301f1d09a5bf3b542d24b3875e359