Remove section about mixing PUSH and POP (#204)

This section is not needed as it describes what can be considered normal GraphQL usage.

Author: mjfwebb

modules/ROOT/pages/mutations/update.adoc

@@ -398,56 +398,6 @@ a|
 |===
 ====
 
-=== Mixing `_PUSH` and `_POP`
-
-It is possible to perform both a `_PUSH` and `_POP` operation in one single `update` mutation.
-
-Consider the following type definitions:
-
-[source, graphql, indent=0]
-----
-type Movie {
-    title: String
-    tags: [String]
-    moreTags: [String]
-}
-----
-
-You can update both property arrays with either `_PUSH` or `_POP` operators at once:
-
-.Mutation with both a `_PUSH` and a `_POP`
-====
-[source, graphql, indent=0]
-----
-mutation {
-    updateMovies (update: { tags_POP: 1, moreTags_PUSH: "a different tag" }) {
-        movies {
-            title
-            tags
-            moreTags
-        }
-    }
-}
-----
-
-[col=1,1]
-|===
-| Before | After
-
-a|
-```
-    tags: ['some tag']
-    moreTags: []
-```
-
-a|
-```
-    tags: []
-    moreTags ['a different tag']
-```
-|===
-====
-
 == Mathematical operators
 
 You can use mathematical operators to update numerical fields based on their original values in a single DB transaction.