Elide lifetimes in more places

Versions of clippy after the MSRV complain about these, and it's fine
on our current Rust version too.

src/diff/graph.rs

@@ -63,7 +63,7 @@ pub(crate) struct Vertex<'s, 'b> {
     rhs_parent_id: Option<SyntaxId>,
 }
 
-impl<'s, 'b> PartialEq for Vertex<'s, 'b> {
+impl PartialEq for Vertex<'_, '_> {
     fn eq(&self, other: &Self) -> bool {
         // Strictly speaking, we should compare the whole
         // EnteredDelimiter stack, not just the immediate
@@ -101,9 +101,9 @@ impl<'s, 'b> PartialEq for Vertex<'s, 'b> {
         b0 && b1 && b2
     }
 }
-impl<'s, 'b> Eq for Vertex<'s, 'b> {}
+impl Eq for Vertex<'_, '_> {}
 
-impl<'s, 'b> Hash for Vertex<'s, 'b> {
+impl Hash for Vertex<'_, '_> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.lhs_syntax.map(|node| node.id()).hash(state);
         self.rhs_syntax.map(|node| node.id()).hash(state);
@@ -132,7 +132,7 @@ enum EnteredDelimiter<'s, 'b> {
     PopBoth((&'s Syntax<'s>, &'s Syntax<'s>)),
 }
 
-impl<'s, 'b> fmt::Debug for EnteredDelimiter<'s, 'b> {
+impl fmt::Debug for EnteredDelimiter<'_, '_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let desc = match self {
             EnteredDelimiter::PopEither((lhs_delims, rhs_delims)) => {

src/diff/sliders.rs

@@ -621,7 +621,7 @@ fn distance_between(prev: &Syntax, next: &Syntax) -> (u32, u32) {
     (0, 0)
 }
 
-impl<'a> Syntax<'a> {
+impl Syntax<'_> {
     fn first_line_span(&self) -> Option<SingleLineSpan> {
         match self {
             List {

src/display/json.rs

@@ -170,7 +170,7 @@ impl<'f> From<&'f DiffResult> for File<'f> {
     }
 }
 
-impl<'f> Serialize for File<'f> {
+impl Serialize for File<'_> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,

src/parse/syntax.rs

@@ -22,7 +22,7 @@ use crate::{
 /// A Debug implementation that does not recurse into the
 /// corresponding node mentioned for Unchanged. Otherwise we will
 /// infinitely loop on unchanged nodes, which both point to the other.
-impl<'a> fmt::Debug for ChangeKind<'a> {
+impl fmt::Debug for ChangeKind<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let desc = match self {
             Unchanged(node) => format!("Unchanged(ID: {})", node.id()),
@@ -91,7 +91,7 @@ impl<'a> SyntaxInfo<'a> {
     }
 }
 
-impl<'a> Default for SyntaxInfo<'a> {
+impl Default for SyntaxInfo<'_> {
     fn default() -> Self {
         Self::new()
     }
@@ -591,7 +591,7 @@ fn set_num_ancestors(nodes: &[&Syntax], num_ancestors: u32) {
     }
 }
 
-impl<'a> PartialEq for Syntax<'a> {
+impl PartialEq for Syntax<'_> {
     fn eq(&self, other: &Self) -> bool {
         debug_assert!(self.content_id() > 0);
         debug_assert!(other.content_id() > 0);