DOC-5601 Remove functions topics (#71)

* combine transform function refs and delete most

* delete transform functions page

Author: aimurphy

modules/ROOT/nav.adoc

@@ -31,15 +31,5 @@
 *** xref:pulsar-io:connectors/sinks/kafka.adoc[]
 *** xref:pulsar-io:connectors/sinks/kinesis.adoc[]
 *** xref:pulsar-io:connectors/sinks/snowflake.adoc[]
-* xref:functions:astream-functions.adoc[]
-* Transformation Functions
-** xref:functions:index.adoc[]
-** xref:functions:cast.adoc[]
-** xref:functions:compute.adoc[]
-** xref:functions:drop.adoc[]
-** xref:functions:flatten.adoc[]
-** xref:functions:merge-key-value.adoc[]
-** xref:functions:unwrap-key-value.adoc[]
-** xref:functions:deploy-in-sink.adoc[]
-** xref:functions:drop-fields.adoc[]
+* xref:astra-streaming:developing:astream-functions.adoc[{pulsar-short} functions]
 * xref:astra-streaming:ROOT:astream-subscriptions.adoc[Topic subscriptions]