MAINT: revert the change

Signed-off-by: George Chen <[email protected]>

data-prepper-plugins/mutate-event-processors/src/main/java/org/opensearch/dataprepper/plugins/processor/mutateevent/ListToMapProcessorConfig.java

@@ -13,7 +13,6 @@
 import com.fasterxml.jackson.annotation.JsonValue;
 import jakarta.validation.constraints.NotEmpty;
 import jakarta.validation.constraints.NotNull;
-import org.opensearch.dataprepper.model.annotations.AlsoRequired;
 
 import java.util.Arrays;
 import java.util.List;
@@ -24,8 +23,6 @@
 @JsonClassDescription("The <code>list_to_map</code> processor converts a list of objects from an event, " +
         "where each object contains a <code>key</code> field, into a map of target keys.")
 public class ListToMapProcessorConfig {
-    static final String KEY_KEY = "key";
-
     public enum FlattenedElement {
         FIRST("first"),
         LAST("last");
@@ -67,12 +64,9 @@ public String getOptionValue() {
     @JsonProperty("use_source_key")
     @JsonPropertyDescription("When <code>true</code>, keys in the generated map will use original keys from the source. " +
             "Default is <code>false</code>.")
-    @AlsoRequired(values = {
-            @AlsoRequired.Required(name = KEY_KEY)
-    })
     private boolean useSourceKey = false;
 
-    @JsonProperty(KEY_KEY)
+    @JsonProperty("key")
     @JsonPropertyDescription("The key of the fields to be extracted as keys in the generated mappings. Must be " +
             "specified if <code>use_source_key</code> is <code>false</code>.")
     private String key;