Remove leftover transport module docs (#42734)

This commit removes docs for alternate transport implementations which
were removed years ago. These were missed because they have redirects
masking their existsence.

docs/reference/modules/memcached.asciidoc

@@ -1,69 +0,0 @@
-[[modules-memcached]]
-== memcached
-
-The memcached module allows to expose *Elasticsearch*
-APIs over the memcached protocol (as closely
-as possible).
-
-It is provided as a plugin called `transport-memcached` and installing
-is explained
-https://github.com/elastic/elasticsearch-transport-memcached[here]
-. Another option is to download the memcached plugin and placing it
-under the `plugins` directory.
-
-The memcached protocol supports both the binary and the text protocol,
-automatically detecting the correct one to use.
-
-[float]
-=== Mapping REST to Memcached Protocol
-
-Memcached commands are mapped to REST and handled by the same generic
-REST layer in Elasticsearch. Here is a list of the memcached commands
-supported:
-
-[float]
-==== GET
-
-The memcached `GET` command maps to a REST `GET`. The key used is the
-URI (with parameters). The main downside is the fact that the memcached
-`GET` does not allow body in the request (and `SET` does not allow to
-return a result...). For this reason, most REST APIs (like search) allow
-to accept the "source" as a URI parameter as well.
-
-[float]
-==== SET
-
-The memcached `SET` command maps to a REST `POST`. The key used is the
-URI (with parameters), and the body maps to the REST body.
-
-[float]
-==== DELETE
-
-The memcached `DELETE` command maps to a REST `DELETE`. The key used is
-the URI (with parameters).
-
-[float]
-==== QUIT
-
-The memcached `QUIT` command is supported and disconnects the client.
-
-[float]
-=== Settings
-
-The following are the settings the can be configured for memcached:
-
-[cols="<,<",options="header",]
-|===============================================================
-|Setting |Description
-|`memcached.port` |A bind port range. Defaults to `11211-11311`.
-|===============================================================
-
-It also uses the common
-<<modules-network,network settings>>.
-
-[float]
-=== Disable memcached
-
-The memcached module can be completely disabled and not started using by
-setting `memcached.enabled` to `false`. By default it is enabled once it
-is detected as a plugin.

docs/reference/modules/thrift.asciidoc

@@ -1,25 +0,0 @@
-[[modules-thrift]]
-== Thrift
-
-The https://thrift.apache.org/[thrift] transport module allows to expose the REST interface of
-Elasticsearch using thrift. Thrift should provide better performance
-over http. Since thrift provides both the wire protocol and the
-transport, it should make using Elasticsearch more efficient (though it has limited
-documentation).
-
-Using thrift requires installing the `transport-thrift` plugin, located
-https://github.com/elastic/elasticsearch-transport-thrift[here].
-
-The thrift
-https://github.com/elastic/elasticsearch-transport-thrift/blob/master/elasticsearch.thrift[schema]
-can be used to generate thrift clients.
-
-[cols="<,<",options="header",]
-|=======================================================================
-|Setting |Description
-|`thrift.port` |The port to bind to. Defaults to 9500-9600
-
-|`thrift.frame` |Defaults to `-1`, which means no framing. Set to a
-higher value to specify the frame size (like `15mb`).
-|=======================================================================
-