Remove Pub/Sub from the Cloud Explorer.

[ILMTitan]

Fixes #945

[redborian]

LGTM

[codecov]

Codecov Report

Merging #971 into master will decrease coverage by 2.14%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #971      +/-   ##
==========================================
- Coverage   37.71%   35.57%   -2.15%     
==========================================
  Files         487      458      -29     
  Lines       11839    11248     -591     
==========================================
- Hits         4465     4001     -464     
+ Misses       7374     7247     -127

Impacted Files	Coverage Δ
...oogleCloudExtension/GoogleCloudExtensionPackage.cs	62.65% <ø> (ø)	⬆️
...dExtension/CloudExplorer/CloudExplorerViewModel.cs	75% <ø> (-0.52%)	⬇️
...oogleCloudExtension/Utils/ProtectedAsyncCommand.cs	100% <100%> (ø)	⬆️
...ogleCloudExtension/Utils/PropertyWindowItemBase.cs	0% <0%> (-41.18%)	⬇️
...sion/CloudExplorer/CloudExplorerSourceException.cs	25% <0%> (-25%)	⬇️
...sion/GoogleCloudExtension/Utils/UserPromptUtils.cs	54.71% <0%> (-22.65%)	⬇️
...oogleCloudExtension/UserPrompt/UserPromptWindow.cs	40% <0%> (-6.67%)	⬇️
...GoogleCloudExtension.DataSources/DataSourceBase.cs	96.66% <0%> (-3.34%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cc74085...8ffad68. Read the comment docs.