Remove use of similarity in KeywordProperty tests

This commit removes the use of similarity in
KeywordProperty tests as it is causing
integration test failures on CI.

Upstream changes in Elasticsearch are being made to
mappings which should be addressed in the client
mappings as part of #3145.

(cherry picked from commit 5062883)

Author: russcam

tests/Tests/Mapping/Types/Core/Keyword/KeywordPropertyTests.cs

@@ -33,7 +33,6 @@ public KeywordPropertyTests(WritableCluster cluster, EndpointUsage usage) : base
 					index_options = "freqs",
 					null_value = "null",
 					norms = false,
-					similarity = "BM25",
 					fields = new
 					{
 						foo = new
@@ -60,7 +59,6 @@ public KeywordPropertyTests(WritableCluster cluster, EndpointUsage usage) : base
 				.NullValue("null")
 				.Normalizer("myCustom")
 				.Norms(false)
-				.Similarity("BM25")
 				.Store()
 				.Fields(fs => fs
 					.Keyword(k => k
@@ -85,7 +83,6 @@ public KeywordPropertyTests(WritableCluster cluster, EndpointUsage usage) : base
 					NullValue = "null",
 					Normalizer = "myCustom",
 					Norms = false,
-					Similarity = "BM25",
 					Store = true,
 					Fields = new Properties
 					{