Removing deprecated ServiceAccount creation in StorageImplTest.

[sduskis]

Fixes #<issue_number_goes_here> (it's a good idea to open an issue first for context and/or discussion)

[codecov]

Codecov Report

Merging #4490 into master will decrease coverage by 0.63%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #4490      +/-   ##
============================================
- Coverage     49.16%   48.52%   -0.64%     
+ Complexity    21915    20739    -1176     
============================================
  Files          2078     2078              
  Lines        207082   203004    -4078     
  Branches      24084    23291     -793     
============================================
- Hits         101804    98517    -3287     
+ Misses        97135    96437     -698     
+ Partials       8143     8050      -93

Impacted Files	Coverage Δ	Complexity Δ
...in/java/com/google/cloud/storage/StorageBatch.java	88% <0%> (-4%)	13% <0%> (ø)
...m/google/cloud/vision/v1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
...e/cloud/vision/v1p3beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
...e/cloud/vision/v1p2beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
.../java/com/google/cloud/speech/v1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...om/google/cloud/speech/v1p1beta1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...ogle/cloud/texttospeech/v1/TextToSpeechClient.java	55.88% <0%> (-2.46%)	9% <0%> (-2%)
...cloud/texttospeech/v1beta1/TextToSpeechClient.java	55.88% <0%> (-2.46%)	9% <0%> (-2%)
.../src/main/java/com/google/cloud/AsyncPageImpl.java	64.28% <0%> (-2.39%)	2% <0%> (ø)
...gle/cloud/storage/testing/RemoteStorageHelper.java	55.37% <0%> (-2.36%)	8% <0%> (ø)
... and 484 more

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[igorbernstein2]

LGTM