Removed methods deprecated in GDAL3.6 (MINOR)

[BlakeOrth]

• Removed the usage of VSISetCredential and VSIClearCredential that have been deprecated in GDAL 3.6

[BlakeOrth]

Well, I guess this needs to wait for Alpine's packages to catch up.

[codecov[bot]]

Codecov Report

Merging #14 (89c5769) into main (be9737e) will not change coverage. The diff coverage is 0.00%.

@@          Coverage Diff          @@
##            main     #14   +/-   ##
=====================================
  Coverage   4.94%   4.94%           
=====================================
  Files          7       7           
  Lines       3152    3152           
=====================================
  Hits         156     156           
  Misses      2990    2990           
  Partials       6       6           

Files Changed	Coverage Δ
gdal.go	7.12% <0.00%> (ø)

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