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-protocol/src/engine/stack.rs

@@ -45,8 +45,6 @@ pub struct Stack {
     pub arguments: ArgumentStack,
     /// Error handler stack for IR evaluation
     pub error_handlers: ErrorHandlerStack,
-    /// Set true to always use IR mode
-    pub use_ir: bool,
     pub recursion_count: u64,
     pub parent_stack: Option<Arc<Stack>>,
     /// Variables that have been deleted (this is used to hide values from parent stack lookups)
@@ -78,7 +76,6 @@ impl Stack {
             active_overlays: vec![DEFAULT_OVERLAY_NAME.to_string()],
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
-            use_ir: true,
             recursion_count: 0,
             parent_stack: None,
             parent_deletions: vec![],
@@ -99,7 +96,6 @@ impl Stack {
             active_overlays: parent.active_overlays.clone(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
-            use_ir: parent.use_ir,
             recursion_count: parent.recursion_count,
             vars: vec![],
             parent_deletions: vec![],
@@ -317,7 +313,6 @@ impl Stack {
             active_overlays: self.active_overlays.clone(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
-            use_ir: self.use_ir,
             recursion_count: self.recursion_count,
             parent_stack: None,
             parent_deletions: vec![],
@@ -351,7 +346,6 @@ impl Stack {
             active_overlays: self.active_overlays.clone(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
-            use_ir: self.use_ir,
             recursion_count: self.recursion_count,
             parent_stack: None,
             parent_deletions: vec![],