remove cp-old (#11622)

# Description

The `cp-old` command has been deprecated for a few releases now. It
should be safe to remove it once and for all. Let's see.

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crates/nu-command/src/default_context.rs

@@ -206,7 +206,6 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Mktemp,
             Mv,
             UMv,
-            Cp,
             UCp,
             Open,
             Start,