chore: Remove low-level ffi/jvm timers from native ScanExec

[andygrove]

Which issue does this PR close?

N/A

Rationale for this change

These timers were useful in the past but I don't remember the last time I looked at these metrics.

What changes are included in this PR?

How are these changes tested?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.63%. Comparing base (f09f8af) to head (2a1ba45).
⚠️ Report is 781 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2939      +/-   ##
============================================
+ Coverage     56.12%   59.63%   +3.50%     
- Complexity      976     1379     +403     
============================================
  Files           119      167      +48     
  Lines         11743    15459    +3716     
  Branches       2251     2559     +308     
============================================
+ Hits           6591     9219    +2628     
- Misses         4012     4946     +934     
- Partials       1140     1294     +154     

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[mbutrovich]

Looks good to me, thanks @andygrove!

[hsiang-c]

LGTM