src: remove unused BindingData::LoadEnvFile declaration

[Archkon]

LoadEnvFile is implemented and registered as a file-local function, not a BindingData static member. Remove the unused member declaration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.28%. Comparing base (cd78d08) to head (69fcfff).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #65001   +/-   ##
=======================================
  Coverage   90.28%   90.28%           
=======================================
  Files         762      762           
  Lines      247534   247532    -2     
  Branches    46684    46682    -2     
=======================================
+ Hits       223479   223486    +7     
- Misses      15485    15490    +5     
+ Partials     8570     8556   -14     

Files with missing lines	Coverage Δ
src/node_process.h	100.00% <ø> (ø)

... and 33 files with indirect coverage changes

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