Remove the NU_DISABLE_IR option (#14293)

# Description

Removes the `NU_DISABLE_IR` option and some code related to evaluating
blocks with the AST
evaluator.

Does not entirely remove the AST evaluator yet. We still have some
dependencies on expression
evaluation in a few minor places which will take a little bit of effort
to fix.

Also changes `debug profile` to always include instructions, because the
output is a little
confusing otherwise, and removes the different options for
instructions/exprs.

# User-Facing Changes

- `NU_DISABLE_IR` no longer has any effect, and is removed. There is no
way to use the AST
  evaluator.
- `debug profile` no longer has `--exprs`, `--instructions` options.
- `debug profile` lists `pc` and `instruction` columns by default now.

# Tests + Formatting

Eval tests fixed to only use IR.

# After Submitting

- [ ] release notes
- [ ] finish removing AST evaluator, come up with solutions for the
expression evaluation.

crates/nu-test-support/src/macros.rs

@@ -248,7 +248,6 @@ pub struct NuOpts {
     pub locale: Option<String>,
     pub envs: Option<Vec<(String, String)>>,
     pub collapse_output: Option<bool>,
-    pub use_ir: Option<bool>,
     // Note: At the time this was added, passing in a file path was more convenient. However,
     // passing in file contents seems like a better API - consider this when adding new uses of
     // this field.
@@ -301,15 +300,6 @@ pub fn nu_run_test(opts: NuOpts, commands: impl AsRef<str>, with_std: bool) -> O
         .stdout(Stdio::piped())
         .stderr(Stdio::piped());
 
-    // Explicitly set NU_DISABLE_IR
-    if let Some(use_ir) = opts.use_ir {
-        if !use_ir {
-            command.env("NU_DISABLE_IR", "1");
-        } else {
-            command.env_remove("NU_DISABLE_IR");
-        }
-    }
-
     // Uncomment to debug the command being run:
     // println!("=== command\n{command:?}\n");