lint: Remove unused 'pluginName' to fix lint error

[t-kikuc]

What this PR does:

as title

Why we need it:

To suppress this lint error:

INFO [runner] linters took 535.982544ms with stages: goanalysis_metalinter: 534.031616ms 
deployment.go:417:36: `newPipelineSyncStagesResponse` - `pluginName` is unused (unparam)
func newPipelineSyncStagesResponse(pluginName string, now time.Time, request *deployment.BuildPipelineSyncStagesRequest, response *BuildPipelineSyncStagesResponse) (*deployment.BuildPipelineSyncStagesResponse, error) {
               

The cause: #6004 removed unused Name() and pluginName became unused.

Which issue(s) this PR fixes:

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

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 28.19%. Comparing base (038a2c6) to head (cb512df).
⚠️ Report is 361 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/plugin/sdk/deployment.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6007   +/-   ##
=======================================
  Coverage   28.19%   28.19%           
=======================================
  Files         520      520           
  Lines       56011    56011           
=======================================
  Hits        15790    15790           
  Misses      38970    38970           
  Partials     1251     1251           

Flag	Coverage Δ
.	23.22% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	66.27% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.33% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	80.26% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	50.71% <80.00%> (ø)
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.30% <ø> (ø)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (ø)

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[khanhtc1202]

Nice catch 👍

[Warashi]

LGTM