fix: remove unused COPY_SECUREFILEDROP_LINK socket command

[Rello]

Motivation

• Reduce the exposed/unnecessary socket API surface by removing an unsecured socket endpoint that had no producers or call sites in the codebase.

Description

• Removed COPY_SECUREFILEDROP_LINK from the FinderSync allow-list in src/gui/macOS/findersyncservice.mm so the macOS extension can no longer invoke it.
• Removed the Q_INVOKABLE declaration for command_COPY_SECUREFILEDROP_LINK from src/gui/socketapi/socketapi.h.
• Removed the SocketApi::command_COPY_SECUREFILEDROP_LINK implementation from src/gui/socketapi/socketapi.cpp.

Testing

• Verified there are no remaining references by searching for COPY_SECUREFILEDROP_LINK and command_COPY_SECUREFILEDROP_LINK with rg, which returned no hits after the change (success).
• Inspected related helpers such as GetOrCreatePublicLinkShare to ensure no dependent behavior was removed (manual code inspection, success).
• Attempted xcodebuild build -target NextcloudDev as recommended for macOS build verification but the environment lacks xcodebuild, so a full macOS build could not be run here (not executed).

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Codex Task

[mgallien]

/backport to stable-33.0

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-9808.zip

Digest: sha256:986ac613ad1c6e9e9b4aea081b50b83c573ce088faee48eed7ecfb97a0e0d357

To test this change/fix you can download the above artifact file, unzip it, and run it.

Please make sure to quit your existing Nextcloud app and backup your data.

[sonarqubecloud]

Quality Gate failed

Failed conditions
29 New Code Smells (required ≤ 0)

See analysis details on SonarQube Cloud

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[backportbot]

The backport to stable-33.0 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable-33.0
git pull origin stable-33.0

# Create the new backport branch
git checkout -b backport/9808/stable-33.0

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 3574314d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/9808/stable-33.0

Error: Failed to check for changes with origin/stable-33.0: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[nilsding]

/backport to stable-33.0

[backportbot]

The backport to stable-33.0 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable-33.0
git pull origin stable-33.0

# Create the new backport branch
git checkout -b backport/9808/stable-33.0

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 3574314d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/9808/stable-33.0

Error: Failed to check for changes with origin/stable-33.0: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.