Revert "Add l2_norm normalization support to linear retriever (#128504)"

This reverts commit 81fba27.

Author: mridula-s109

docs/changelog/128504.yaml

@@ -276,7 +276,7 @@ Each entry specifies the following parameters:
 `normalizer`
 :   (Optional, String)
 
-    - Specifies how we will normalize the retriever’s scores, before applying the specified `weight`. Available values are: `minmax`, `l2_norm`, and `none`. Defaults to `none`.
+    Specifies how we will normalize the retriever’s scores, before applying the specified `weight`. Available values are: `minmax`, and `none`. Defaults to `none`.
 
     * `none`
     * `minmax` : A `MinMaxScoreNormalizer` that normalizes scores based on the following formula
@@ -285,7 +285,6 @@ Each entry specifies the following parameters:
         score = (score - min) / (max - min)
         ```
 
-    * `l2_norm` : An `L2ScoreNormalizer` that normalizes scores using the L2 norm of the score values.
 
 See also [this hybrid search example](docs-content://solutions/search/retrievers-examples.md#retrievers-examples-linear-retriever) using a linear retriever on how to independently configure and apply normalizers to retrievers.
 

docs/reference/elasticsearch/rest-apis/retrievers.md

@@ -17,9 +17,6 @@ public abstract class ScoreNormalizer {
     public static ScoreNormalizer valueOf(String normalizer) {
         if (MinMaxScoreNormalizer.NAME.equalsIgnoreCase(normalizer)) {
             return MinMaxScoreNormalizer.INSTANCE;
-        } else if (L2ScoreNormalizer.NAME.equalsIgnoreCase(normalizer)) {
-            return L2ScoreNormalizer.INSTANCE;
-
         } else if (IdentityScoreNormalizer.NAME.equalsIgnoreCase(normalizer)) {
             return IdentityScoreNormalizer.INSTANCE;
 

x-pack/plugin/rank-rrf/src/main/java/org/elasticsearch/xpack/rank/linear/L2ScoreNormalizer.java

@@ -265,93 +265,6 @@ setup:
   - match: { hits.hits.3._id: "3" }
   - close_to: { hits.hits.3._score: { value: 0.0, error: 0.001 } }
 
----
-"should normalize initial scores with l2_norm":
-  - do:
-      search:
-        index: test
-        body:
-          retriever:
-            linear:
-              retrievers: [
-                {
-                  retriever: {
-                    standard: {
-                      query: {
-                        bool: {
-                          should: [
-                            { constant_score: { filter: { term: { keyword: { value: "one" } } }, boost: 3.0 } },
-                            { constant_score: { filter: { term: { keyword: { value: "two" } } }, boost: 4.0 } }
-                          ]
-                        }
-                      }
-                    }
-                  },
-                  weight: 10.0,
-                  normalizer: "l2_norm"
-                },
-                {
-                  retriever: {
-                    standard: {
-                      query: {
-                        bool: {
-                          should: [
-                            { constant_score: { filter: { term: { keyword: { value: "three" } } }, boost: 6.0 } },
-                            { constant_score: { filter: { term: { keyword: { value: "four" } } }, boost: 8.0 } }
-                          ]
-                        }
-                      }
-                    }
-                  },
-                  weight: 2.0,
-                  normalizer: "l2_norm"
-                }
-              ]
-
-  - match: { hits.total.value: 4 }
-  - match: { hits.hits.0._id: "2" }
-  - match: { hits.hits.0._score: 8.0 }
-  - match: { hits.hits.1._id: "1" }
-  - match: { hits.hits.1._score: 6.0 }
-  - match: { hits.hits.2._id: "4" }
-  - close_to: { hits.hits.2._score: { value: 1.6, error: 0.001 } }
-  - match: { hits.hits.3._id: "3" }
-  - match: { hits.hits.3._score: 1.2 }
-
----
-"should handle all zero scores in normalization":
-  - do:
-      search:
-        index: test
-        body:
-          retriever:
-            linear:
-              retrievers: [
-                {
-                  retriever: {
-                    standard: {
-                      query: {
-                        bool: {
-                          should: [
-                            { constant_score: { filter: { term: { keyword: { value: "one" } } }, boost: 0.0 } },
-                            { constant_score: { filter: { term: { keyword: { value: "two" } } }, boost: 0.0 } },
-                            { constant_score: { filter: { term: { keyword: { value: "three" } } }, boost: 0.0 } },
-                            { constant_score: { filter: { term: { keyword: { value: "four" } } }, boost: 0.0 } }
-                          ]
-                        }
-                      }
-                    }
-                  },
-                  weight: 1.0,
-                  normalizer: "l2_norm"
-                }
-              ]
-  - match: { hits.total.value: 4 }
-  - close_to: { hits.hits.0._score: { value: 0.0, error: 0.0001 } }
-  - close_to: { hits.hits.1._score: { value: 0.0, error: 0.0001 } }
-  - close_to: { hits.hits.2._score: { value: 0.0, error: 0.0001 } }
-  - close_to: { hits.hits.3._score: { value: 0.0, error: 0.0001 } }
-
 ---
 "should throw on unknown normalizer":
   - do: