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/tests/commands/move_/mod.rs

@@ -1,3 +1,2 @@
 mod column;
-mod mv;
 mod umv;