Revert "Reindex source types disregarded in 7.x"

This reverts commit fabbff1.

Author: jrodewig

docs/reference/docs/reindex.asciidoc

@@ -529,10 +529,6 @@ To preserve other document types, this parameter must be specified.
 (Optional, enum) The script language: `painless`, `expression`, `mustache`, `java`. 
 For more information, see <<modules-scripting>>.
 
-NOTE: Types in source indices are always ignored, also when not specifying a
-destination `type`. If explicitly specifying destination `type`, the specified
-type must match the type in the destination index or be either unspecified or
-the special value `_doc`. See <<removal-of-types>> for further details.
 
 [[docs-reindex-api-response-body]]
 ==== {api-response-body-title}