The `workspaceLoaded` notification setting was originally designed to
control the display of a popup message that said:
"workspace loaded, {} rust packages"
This popup was removed and replaced by a much sleeker message in the
VSCode status bar that provides a real-time status while loading:
rust-analyzer: {}/{} packages
This was done as part of #3587
The new status-bar indicator is unobtrusive and shouldn't need to be
disabled. So this setting is removed.
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