Remove prefix --experimental- instead of --experimental from flag

[ahrtr]

Otherwise, we will get flags something like below when converting experimental flag to non-experimental flag,

• ---compaction-batch-limit=10
• ---watch-progress-notify-interval=100ms

See errors below,

    main_test.go:144: failed triggering failpoint, err: failed to find etcd ready lines ["ready to serve client requests"], err: match not found.  Set EXPECT_DEBUG for more info Errs: [unexpected exit code [2] after running [/tmp/etcd-release-3.6-failpoints/bin/etcd --name=TestRobustnessExploratoryKubernetesLowTrafficClusterOfSize1-test-0 --listen-client-urls=http://localhost:20000 --advertise-client-urls=http://localhost:20000 --listen-peer-urls=http://localhost:20001 --initial-advertise-peer-urls=http://localhost:20001 --initial-cluster-token=new --data-dir=/tmp/TestRobustnessExploratoryKubernetesLowTrafficClusterOfSize13155801533/001 --snapshot-count=1000 --snapshot-count=1000 ---compaction-batch-limit=1000 ---watch-progress-notify-interval=100ms --initial-cluster-token=new --initial-cluster=TestRobustnessExploratoryKubernetesLowTrafficClusterOfSize1-test-0=http://localhost:20001 --initial-cluster-state=new]], last lines:
        bad flag syntax: ---compaction-batch-limit=1000
        Usage:
        
          etcd [flags]
            Start an etcd server.
        
          etcd --version
            Show the version of etcd.
        
          etcd -h | --help
            Show the help information about etcd.
        
          etcd --config-file
            Path to the server configuration file. Note that if a configuration file is provided, other command line flags and environment variables will be ignored.
        
          etcd gateway
            Run the stateless pass-through etcd TCP connection forwarding proxy.
        
          etcd grpc-proxy
            Run the stateless etcd v3 gRPC L7 reverse proxy.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[ahrtr]

followup to #20001

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.00%. Comparing base (ebcfdd0) to head (96e40b2).
Report is 2 commits behind head on main.

Additional details and impacted files

see 144 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #20019      +/-   ##
==========================================
- Coverage   68.74%   62.00%   -6.74%     
==========================================
  Files         424      412      -12     
  Lines       35757    34663    -1094     
==========================================
- Hits        24580    21493    -3087     
- Misses       9761    11594    +1833     
- Partials     1416     1576     +160     

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[ahrtr]

All other PRs are affected, we need to get this PR merged asap. cc @fuweid @ivanvc @jmhbnz @serathius Please approve this PR when you get 1 second.

Note: we just merged kubernetes/test-infra#34834 today. Will revert that PR once this PR gets verified & merged.

[jmhbnz]

LGTM - Thanks @ahrtr

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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