Delete parent field on DiagnosticMessage and CacheMessage

Summary
--

Deletes the unused `parent` field on two structs, which should make converting
these to the new `Diagnostic` type a little easier.

It looks like I accidentally added both of these in #16837 in an early commit
that I only partially reverted, so they have never actually been used.

Test Plan
--

Existing tests

Author: ntBre

crates/ruff/src/cache.rs

@@ -353,7 +353,6 @@ impl FileCache {
                             fix: msg.fix.clone(),
                             file: file.clone(),
                             noqa_offset: msg.noqa_offset,
-                            parent: msg.parent,
                         })
                     })
                     .collect()
@@ -446,7 +445,6 @@ impl LintCacheData {
                 CacheMessage {
                     kind: msg.kind.clone(),
                     range: msg.range,
-                    parent: msg.parent,
                     fix: msg.fix.clone(),
                     noqa_offset: msg.noqa_offset,
                 }
@@ -467,7 +465,6 @@ pub(super) struct CacheMessage {
     kind: DiagnosticKind,
     /// Range into the message's [`FileCache::source`].
     range: TextRange,
-    parent: Option<TextSize>,
     fix: Option<Fix>,
     noqa_offset: TextSize,
 }

crates/ruff_linter/src/fix/edits.rs

@@ -749,7 +749,6 @@ x = 1 \
                 kind: diag.kind,
                 range: diag.range,
                 fix: diag.fix,
-                parent: diag.parent,
                 file: SourceFileBuilder::new("<filename>", "<code>").finish(),
                 noqa_offset: TextSize::default(),
             }

crates/ruff_linter/src/fix/mod.rs

@@ -184,7 +184,6 @@ mod tests {
                 kind: MissingNewlineAtEndOfFile.into(),
                 range: edit.range(),
                 fix: Some(Fix::safe_edit(edit)),
-                parent: None,
                 file: SourceFileBuilder::new(filename, source).finish(),
                 noqa_offset: TextSize::default(),
             })

crates/ruff_linter/src/message/mod.rs

@@ -54,7 +54,6 @@ pub struct DiagnosticMessage {
     pub kind: DiagnosticKind,
     pub range: TextRange,
     pub fix: Option<Fix>,
-    pub parent: Option<TextSize>,
     pub file: SourceFile,
     pub noqa_offset: TextSize,
 }
@@ -93,7 +92,6 @@ impl Message {
             range: diagnostic.range(),
             kind: diagnostic.kind,
             fix: diagnostic.fix,
-            parent: diagnostic.parent,
             file,
             noqa_offset,
         })

crates/ruff_linter/src/noqa.rs

@@ -862,26 +862,6 @@ fn find_noqa_comments<'a>(
             }
         }
 
-        // Is the violation ignored by a `noqa` directive on the parent line?
-        if let Some(parent) = diagnostic.parent {
-            if let Some(directive_line) =
-                directives.find_line_with_directive(noqa_line_for.resolve(parent))
-            {
-                match &directive_line.directive {
-                    Directive::All(_) => {
-                        comments_by_line.push(None);
-                        continue;
-                    }
-                    Directive::Codes(codes) => {
-                        if codes.includes(diagnostic.kind.rule()) {
-                            comments_by_line.push(None);
-                            continue;
-                        }
-                    }
-                }
-            }
-        }
-
         let noqa_offset = noqa_line_for.resolve(diagnostic.range.start());
 
         let rule = diagnostic.kind.rule();