Switch citations to using bracket depth from OrgSource instead of from the context.

This is for the same reasons as footnote references.

src/parser/parser_context.rs

@@ -124,21 +124,6 @@ pub enum ContextElement<'r, 's> {
     /// radio links matching the contents of radio targets.
     RadioTarget(Vec<&'r Vec<Object<'s>>>),
 
-    /// Stores the current bracket depth inside a citation.
-    ///
-    /// The global prefix, global suffix, key prefix, and key suffix
-    /// inside a footnote reference must have balanced brackets []
-    /// inside the definition, so this stores the amount of opening
-    /// brackets subtracted by the amount of closing brackets within
-    /// the definition must equal zero. None of the prefixes or
-    /// suffixes can be nested inside each other so we can use a
-    /// single type for this without conflict.
-    ///
-    /// A reference to the position in the string is also included so
-    /// unbalanced brackets can be detected in the middle of an
-    /// object.
-    CitationBracket(CitationBracket<'s>),
-
     /// Stores the current bracket or parenthesis depth inside an inline babel call.
     ///
     /// Inside an inline babel call the headers must have balanced
@@ -183,12 +168,6 @@ pub struct ExitMatcherNode<'r> {
     pub class: ExitClass,
 }
 
-#[derive(Debug)]
-pub struct CitationBracket<'s> {
-    pub position: OrgSource<'s>,
-    pub depth: usize,
-}
-
 #[derive(Debug)]
 pub struct BabelHeaderBracket<'s> {
     pub position: OrgSource<'s>,