delete unused method

[luojiagen]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

Release note:

[codecov]

Codecov Report

Merging #633 (a050034) into vplex_20230329 (c3f0756) will increase coverage by 0.00%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           vplex_20230329     #633   +/-   ##
===============================================
  Coverage           70.85%   70.85%           
===============================================
  Files                 195      195           
  Lines               24001    23991   -10     
  Branches             3678     3675    -3     
===============================================
- Hits                17006    17000    -6     
+ Misses               5833     5826    -7     
- Partials             1162     1165    +3     

Impacted Files	Coverage Δ
delfin/drivers/dell_emc/vplex/vplex_stor.py	79.11% <ø> (+1.42%)	⬆️

... and 1 file with indirect coverage changes