remove old mv command in favor of umv (renamed to mv) (#12022)

# Description

This PR removes our old nushell `mv` command in favor of the
uutils/coreutils `uu_mv` crate's `mv` command which we integrated in
0.90.1.

# User-Facing Changes

# Tests + Formatting

# After Submitting

crates/nu-command/src/default_context.rs

@@ -207,7 +207,6 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Ls,
             UMkdir,
             Mktemp,
-            Mv,
             UMv,
             UCp,
             Open,

crates/nu-command/src/filesystem/mod.rs

@@ -3,7 +3,6 @@ mod du;
 mod glob;
 mod ls;
 mod mktemp;
-mod mv;
 mod open;
 mod rm;
 mod save;
@@ -21,7 +20,6 @@ pub use du::Du;
 pub use glob::Glob;
 pub use ls::Ls;
 pub use mktemp::Mktemp;
-pub use mv::Mv;
 pub use rm::Rm;
 pub use save::Save;
 pub use start::Start;