[DOCS] Remove unneeded redirects (#50476)

The docs/reference/redirects.asciidoc file stores a list of relocated or
deleted pages for the Elasticsearch Reference documentation.

This prunes several older redirects that are no longer needed and
don't require work to fix broken links in other repositories.

docs/reference/how-to/search-speed.asciidoc

@@ -31,7 +31,7 @@ If your search is CPU-bound, you should investigate buying faster CPUs.
 Documents should be modeled so that search-time operations are as cheap as possible.
 
 In particular, joins should be avoided. <<nested,`nested`>> can make queries
-several times slower and <<mapping-parent-field,parent-child>> relations can make
+several times slower and <<parent-join,parent-child>> relations can make
 queries hundreds of times slower. So if the same questions can be answered without
 joins by denormalizing documents, significant speedups can be expected.
 

docs/reference/mapping/removal_of_types.asciidoc

@@ -42,7 +42,7 @@ field, so documents of different types with the same `_id` could exist in a
 single index.
 
 Mapping types were also used to establish a
-<<mapping-parent-field,parent-child relationship>>
+<<parent-join,parent-child relationship>>
 between documents, so documents of type `question` could be parents to
 documents of type `answer`.
 

docs/reference/ml/anomaly-detection/apis/ml-api.asciidoc

@@ -3,9 +3,7 @@
 [[ml-apis]]
 == {ml-cap} {anomaly-detect} APIs
 
-You can use the following APIs to perform {ml} {anomaly-detect} activities. See
-<<ml-api-definitions, Definitions>> for the resource definitions used by the
-machine learning APIs and in advanced job configuration options in Kibana.
+You can use the following APIs to perform {ml} {anomaly-detect} activities.
 
 See also <<ml-df-analytics-apis>>.