Remove rustc_span::HashStableContext::hash_spans.

It reads the `HashingControls::span` field, but there is also the
`hashing_controls` method. No need to have two different ways of doing
it.

compiler/rustc_query_system/src/ich/hcx.rs

@@ -85,11 +85,6 @@ fn hash_stable(&self, _: &mut StableHashingContext<'a>, _: &mut StableHasher) {
 }
 
 impl<'a> rustc_span::HashStableContext for StableHashingContext<'a> {
-    #[inline]
-    fn hash_spans(&self) -> bool {
-        self.hashing_controls.hash_spans
-    }
-
     #[inline]
     fn unstable_opts_incremental_ignore_spans(&self) -> bool {
         self.incremental_ignore_spans

compiler/rustc_span/src/lib.rs

@@ -2799,7 +2799,6 @@ pub fn new(start: usize, end: usize) -> InnerSpan {
 /// instead of implementing everything in rustc_middle.
 pub trait HashStableContext {
     fn def_path_hash(&self, def_id: DefId) -> DefPathHash;
-    fn hash_spans(&self) -> bool;
     /// Accesses `sess.opts.unstable_opts.incremental_ignore_spans` since
     /// we don't have easy access to a `Session`
     fn unstable_opts_incremental_ignore_spans(&self) -> bool;
@@ -2832,7 +2831,7 @@ fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
         const TAG_INVALID_SPAN: u8 = 1;
         const TAG_RELATIVE_SPAN: u8 = 2;
 
-        if !ctx.hash_spans() {
+        if !ctx.hashing_controls().hash_spans {
             return;
         }