Remove unused function (#22848)

Author: Andy

Diff for: src/compiler/core.ts

@@ -623,23 +623,6 @@ namespace ts {
         };
     }
 
-    /**
-     * Computes the first matching span of elements and returns a tuple of the first span
-     * and the remaining elements.
-     */
-    export function span<T>(array: ReadonlyArray<T>, f: (x: T, i: number) => boolean): [T[], T[]] {
-        if (array) {
-            for (let i = 0; i < array.length; i++) {
-                if (!f(array[i], i)) {
-                    return [array.slice(0, i), array.slice(i)];
-                }
-            }
-            return [array.slice(0), []];
-        }
-
-        return undefined;
-    }
-
     /**
      * Maps contiguous spans of values with the same key.
      *