remove size command in favor of str stats (#10784)

follow-up to
- https://github.com/nushell/nushell/pull/10798

> **Important**
> wait for between 0.87 and 0.88 to land this

# Description
once again, after deprecation comes removal 😌 

# User-Facing Changes
`size` is now removed and `str size` should be used

# Tests + Formatting

# After Submitting

crates/nu-command/tests/commands/random/chars.rs

@@ -3,7 +3,7 @@ use nu_test_support::nu;
 #[test]
 fn generates_chars_of_specified_length() {
     let actual = nu!(r#"
-        random chars --length 15 | size | get chars
+        random chars --length 15 | str stats | get chars
         "#);
 
     let result = actual.out;