Remove Observable.sum from core API;

doc/README.md

@@ -34,7 +34,6 @@ RxLua
   - [reject](#rejectpredicate)
   - [skip](#skipn)
   - [skipUntil](#skipuntilother)
-  - [sum](#sum)
   - [take](#taken)
   - [takeUntil](#takeuntilother)
   - [unpack](#unpack)
@@ -451,16 +450,6 @@ Returns:
 
 ---
 
-#### `:sum()`
-
-Returns a new Observable that produces the sum of the values of the original Observable as a single result.
-
-Returns:
-
-- `Observable`
-
----
-
 #### `:take(n)`
 
 Returns a new Observable that only produces the first n results of the original.

rx.lua

@@ -622,13 +622,6 @@ function Observable:skipUntil(other)
   end)
 end
 
---- Returns a new Observable that produces the sum of the values of the original Observable as a
--- single result.
--- @returns {Observable}
-function Observable:sum()
-  return self:reduce(function(x, y) return x + y end, 0)
-end
-
 --- Returns a new Observable that only produces the first n results of the original.
 -- @arg {number=1} n - The number of elements to produce before completing.
 -- @returns {Observable}