move deprecation test to correct 1.6 test file

[awaelchli]

What does this PR do?

This test for hpc_load deprecation was incorrectly placed in the file test_remove_1_4.py but should be in the 1.6 file.

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[codecov]

Codecov Report

Merging #8446 (ef9861d) into master (374fae5) will increase coverage by 4%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #8446    +/-   ##
=======================================
+ Coverage      89%     92%    +4%     
=======================================
  Files         217     217            
  Lines       14223   14223            
=======================================
+ Hits        12605   13128   +523     
+ Misses       1618    1095   -523     

[tchaton]

LGTM!