Revert "feat: expose all the methods of notification"

[frankyn]

Reverts #141

I missed this in review: the surface library shouldn't expose the underlying Google API client object model, specifically line:
https://github.com/athakor/java-storage/blob/300c60459ee91669c20283bcc986737002a9ffb6/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java#L24

Which is used as a return type to CRUD operations:

https://github.com/athakor/java-storage/blob/300c60459ee91669c20283bcc986737002a9ffb6/google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java#L3438-L3468

[codecov]

Codecov Report

Merging #393 into master will decrease coverage by 0.48%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #393      +/-   ##
============================================
- Coverage     63.61%   63.13%   -0.49%     
+ Complexity      632      601      -31     
============================================
  Files            33       32       -1     
  Lines          5222     5078     -144     
  Branches        498      481      -17     
============================================
- Hits           3322     3206     -116     
+ Misses         1730     1708      -22     
+ Partials        170      164       -6     

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/com/google/cloud/storage/Storage.java	80.90% <ø> (ø)	0.00 <0.00> (ø)
...ain/java/com/google/cloud/storage/StorageImpl.java	80.52% <ø> (+0.28%)	131.00 <0.00> (-4.00)	⬆️
...om/google/cloud/storage/spi/v1/HttpStorageRpc.java	1.52% <ø> (+0.01%)	1.00 <0.00> (ø)
...ogle/cloud/storage/spi/v1/HttpStorageRpcSpans.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...va/com/google/cloud/storage/spi/v1/StorageRpc.java	64.86% <ø> (ø)	0.00 <0.00> (ø)
...ogle/cloud/storage/testing/StorageRpcTestBase.java	97.95% <ø> (-0.05%)	48.00 <0.00> (-1.00)

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[athakor]

@frankyn Good catch also i missed it there must be a wrapper instead of underlying Google API client object model