Cleanup unnecessary methods and files for k8s plugin

[ffjlabo]

What this PR does:

As title. I removed some codes for the k8s plugin implemented with the package pkg/plugin directly.

replaced some methods

• applymanifests 498bdef
• determineVersions a5e9204
• buildPipelineStages 927accd
• buildQuickSyncPipeline 5cba9ca
• determineStrategy a15757f

removed files

• sync.go c21c842
• rollback.go c21c842
• server.go fde65bb
• server_test.go bd9b566

Why we need it:

We want to implement plugins with SDK.

Which issue(s) this PR fixes:

Part of #4980 #5006

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

Attention: Patch coverage is 70.37037% with 8 lines in your changes missing coverage. Please review.

Project coverage is 25.65%. Comparing base (20577c0) to head (fde65bb).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...app/pipedv1/plugin/kubernetes/deployment/plugin.go	0.00%	5 Missing and 1 partial ⚠️
.../pipedv1/plugin/kubernetes/deployment/determine.go	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5675      +/-   ##
==========================================
+ Coverage   25.60%   25.65%   +0.05%     
==========================================
  Files         478      474       -4     
  Lines       51307    50905     -402     
==========================================
- Hits        13135    13060      -75     
+ Misses      37167    36854     -313     
+ Partials     1005      991      -14     

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