Revert "Update azure-core version to unbreak Search. (#21599)" (#21610)

This reverts commit 8e98c7f.

Author: tjprescott

shared_requirements.txt

@@ -153,7 +153,7 @@ backports.functools-lru-cache >= 1.6.4; python_version == "2.7"
 #override azure-ai-textanalytics azure-core<2.0.0,>=1.19.1
 #override azure-ai-language-questionanswering azure-core<2.0.0,>=1.19.1
 #override azure-ai-language-questionanswering msrest>=0.6.21
-#override azure-search-documents azure-core<2.0.0,>=1.19.1
+#override azure-search-documents azure-core<2.0.0,>=1.19.0
 #override azure-ai-formrecognizer msrest>=0.6.21
 #override azure-ai-formrecognizer azure-core<2.0.0,>=1.13.0
 #override azure-storage-blob azure-core<2.0.0,>=1.10.0