Remove Gemfire support in Spring Batch

Based on the decision to discontinue the support
of Spring Data for Apache Geode [1], this commit
removes the support for Geode in Spring Batch.

The code will be moved to the spring-batch-extensions
repository as a community-driven effort.

[1]: https://github.com/spring-projects/spring-data-geode#notice

Resolves #4214

spring-batch-docs/src/main/asciidoc/appendix.adoc

@@ -85,9 +85,6 @@ This reader stores message offsets in the execution context to support restart c
             in an injected `List` of `ItemWriter` objects.
 |`FlatFileItemWriter`|Writes to a flat file. Includes `ItemStream` and
             Skippable functionality. See link:readersAndWriters.html#flatFileItemWriter["`FlatFileItemWriter`"].
-|`GemfireItemWriter`|Using a `GemfireOperations` object, items are either written
-            or removed from the Gemfire instance based on the configuration of the delete
-            flag.
 |`HibernateItemWriter`|This item writer is Hibernate-session aware
             and handles some transaction-related work that a non-"`hibernate-aware`"
             item writer would not need to know about and then delegates

spring-batch-docs/src/main/asciidoc/readersAndWriters.adoc

@@ -2933,7 +2933,6 @@ Spring Batch offers the following database writers:
 * <<hibernateItemWriter>>
 * <<jdbcBatchItemWriter>>
 * <<jpaItemWriter>>
-* <<gemfireItemWriter>>
 
 [[neo4jItemWriter]]
 ===== `Neo4jItemWriter`
@@ -2972,12 +2971,6 @@ The `JpaItemWriter` is an `ItemWriter` that uses a JPA `EntityManagerFactory` to
 any entities that are not part of the persistence context. Spring Batch provides a
 `JpaItemWriterBuilder` to construct an instance of the `JpaItemWriter`.
 
-[[gemfireItemWriter]]
-===== `GemfireItemWriter`
-The `GemfireItemWriter` is an `ItemWriter` that uses a `GemfireTemplate` that stores
-items in GemFire as key/value pairs. Spring Batch provides a `GemfireItemWriterBuilder`
-to construct an instance of the `GemfireItemWriter`.
-
 [[specializedReaders]]
 ==== Specialized Readers
 Spring Batch offers the following specialized readers: