Duplicate toolchains in toolchain selection quick pick

[matthewbastien]

Describe the bug
Any installed Swiftly toolchains appear twice in the toolchain selection quick pick. Once under the swiftly label and again under the toolchains label. It would be nice to remove the redundant options under the toolchains label.

To Reproduce
Steps to reproduce the behavior:

1. Install a few different toolchains via Swiftly.
2. Run the Swift: Select Toolchain... command.

You'll notice that the toolchains appear under the swiftly label with just their labels from swiftly list. However, the toolchains that were installed into ~/Developer/Toolchains/ also appear under the toolchains label.

Expected behavior
Toolchains managed by Swiftly should only show up under the swiftly label.

Environment

• OS: macOS
• vscode-swift version: 2.11.20250806

Additional context
Add any other context about the problem here.