docs: Remove references to removed clean command

[Copilot]

Documentation references helm secrets clean command which was removed in v4.0.0, causing user confusion per issue report.

Changes

• Removed "Clean" section from docs/Usage.md describing the non-existent command
• Updated references from "decrypted and cleaned" to "decrypted" where the automatic cleanup is implicit
• Changed "decrypted files are cleaned" to "decrypted files are removed automatically" for clarity

The helm wrapper automatically handles cleanup of decrypted files, making the standalone clean command unnecessary in v4.x.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Cleanup command seems to be broken or missing</issue_title>
<issue_description>### Current Behavior

Using helm secrets clean ${PATH} gets interpreted as helm wrapper command.
Is that part of the wiki outdated, is something broken or am I doing something wrong?

Expected Behavior

According to the wiki at https://github.com/jkroepke/helm-secrets/wiki/Usage#clean there should be a command helm secrets clean ${PATH} to recursively clean up decrypted files (ending with .dec).

Steps To Reproduce

In this folder: <https://github.com/jkroepke/helm-secrets/tree/main/examples/sops>
Using this key: <https://github.com/jkroepke/helm-secrets/blob/main/tests/assets/gpg/private.gpg>

Executing this command:


helm secrets clean ./sops 
Error: unknown command "clean" for "helm"
Run 'helm --help' for usage.
Error: plugin "secrets" exited with error


Checking this help context:



Available Commands:
  encrypt Encrypt secrets file
  decrypt Decrypt secrets file
  edit    Edit secrets file and encrypt afterwards
  dir     Get plugin directory
  <cmd>   wrapper that decrypts encrypted yaml files before running helm <cmd>

Environment

• Helm Version: v4.1.0 (Commit: 4553a0a96e5205595079b6757236cc6f969ed1b9)
• Helm Secrets Version: 4.7.5
• ArgoCD Version: Irrelevant
• OS: Ubuntu 24.04.3 LTS
• Shell: zsh

Anything else?

No response</issue_description>

<agent_instructions>Do not implement the feature, instead cleanup the docs in the docs directory.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@jkroepke It seems the docs are outdated at this point. There is no clean command since helm secrets v4

• Fixes Cleanup command seems to be broken or missing #697

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