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;

crates/nu-command/tests/commands/redirection.rs

@@ -21,7 +21,7 @@ fn redirect_err() {
     Playground::setup("redirect_err_test", |dirs, _sandbox| {
         let output = nu!(
             cwd: dirs.test(),
-            "vol missingdrive err> a; (open a | size).bytes >= 16"
+            "vol missingdrive err> a; (open a | str stats).bytes >= 16"
         );
 
         assert!(output.out.contains("true"));
@@ -50,7 +50,7 @@ fn redirect_outerr() {
             cwd: dirs.test(),
             "vol missingdrive out+err> a"
         );
-        let output = nu!(cwd: dirs.test(), "(open a | size).bytes >= 16");
+        let output = nu!(cwd: dirs.test(), "(open a | str stats).bytes >= 16");
 
         assert!(output.out.contains("true"));
     })