Remove gcs notification tests from Datastream Spanner ITs

[Polber]

Removing these tests as they are redundant as of #1674

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 49.21%. Comparing base (3eccded) to head (2e0aea6). Report is 123 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1815      +/-   ##
============================================
+ Coverage     42.83%   49.21%   +6.38%     
+ Complexity     3424     1226    -2198     
============================================
  Files           824      358     -466     
  Lines         48147    19471   -28676     
  Branches       5168     1955    -3213     
============================================
- Hits          20624     9583   -11041     
+ Misses        25847     9231   -16616     
+ Partials       1676      657    -1019     

Components	Coverage Δ
spanner-templates	62.23% <ø> (-0.58%)	:arrow_down:
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	75.05% <ø> (ø)
spanner-live-reverse-replication	67.63% <ø> (ø)
spanner-bulk-migration	83.75% <ø> (ø)

see 483 files with indirect coverage changes

[manitgupta]

The polling approach has been deprecated in #1674 ; the GCS notification approach is still being actively used. I don't think we should remove this?

[Polber]

#1674

@manitgupta #1674 added a line to make all ITs use GCS notifications

https://github.com/GoogleCloudPlatform/DataflowTemplates/blob/main/v2/datastream-to-spanner/src/test/java/com/google/cloud/teleport/v2/templates/DataStreamToSpannerIT.java#L384

So either that change should be reverted, or this PR should remove the redundant tests