Remove (lots of) dead code

Found with https://github.com/est31/warnalyzer.

Dubious changes:
- Is anyone else using rustc_apfloat? I feel weird completely deleting
  x87 support.
- Maybe some of the dead code in rustc_data_structures, in case someone
  wants to use it in the future?
- Don't change rustc_serialize

  I plan to scrap most of the json module in the near future (see
  https://github.com/rust-lang/compiler-team/issues/418) and fixing the
  tests needed more work than I expected.

TODO: check if any of the comments on the deleted code should be kept.

compiler/rustc_hir/src/pat_util.rs

@@ -89,26 +89,6 @@ impl hir::Pat<'_> {
         })
     }
 
-    /// Checks if the pattern contains any patterns that bind something to
-    /// an ident, e.g., `foo`, or `Foo(foo)` or `foo @ Bar(..)`.
-    pub fn contains_bindings(&self) -> bool {
-        self.satisfies(|p| matches!(p.kind, PatKind::Binding(..)))
-    }
-
-    /// Checks if the pattern satisfies the given predicate on some sub-pattern.
-    fn satisfies(&self, pred: impl Fn(&hir::Pat<'_>) -> bool) -> bool {
-        let mut satisfies = false;
-        self.walk_short(|p| {
-            if pred(p) {
-                satisfies = true;
-                false // Found one, can short circuit now.
-            } else {
-                true
-            }
-        });
-        satisfies
-    }
-
     pub fn simple_ident(&self) -> Option<Ident> {
         match self.kind {
             PatKind::Binding(