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-cmd-lang/src/core_commands/do_.rs

@@ -82,9 +82,6 @@ impl Command for Do {
         bind_args_to(&mut callee_stack, &block.signature, rest, head)?;
         let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
 
-        // Applies to all block evaluation once set true
-        callee_stack.use_ir = !caller_stack.has_env_var(engine_state, "NU_DISABLE_IR");
-
         let result = eval_block_with_early_return(engine_state, &mut callee_stack, block, input);
 
         if has_env {