Revert "stdlib: Mark many higher-order function interfaces as 'rethrows'."

This reverts commit r30597, to help detangle it from other potentially-breaking changes that landed
on the bots simultaneously.

Swift SVN r30602

stdlib/public/core/CollectionAlgorithms.swift.gyb

@@ -57,10 +57,10 @@ extension CollectionType {
   ///
   /// - Complexity: O(`self.count`).
   public func indexOf(
-    @noescape predicate: (${GElement}) throws -> Bool
-  ) rethrows -> Index? {
+    @noescape predicate: (${GElement}) -> Bool
+  ) -> Index? {
     for i in self.indices {
-      if try predicate(self[i]) {
+      if predicate(self[i]) {
         return i
       }
     }