Remove specifying provisioned throughput for GSIs (aws#3923)

* If there's no information about the billing mode of the new table,
  then it'll be using the PAY_PER_REQUEST one. It means that all
  GSIs related to this table will be doing the same and there's
  no need to hard code any provisioned throughput like it was done

Author: Adrian Chlebosz

services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/client/DefaultDynamoDbTable.java

@@ -169,7 +169,6 @@ private EnhancedGlobalSecondaryIndex mapIndexMetadataToEnhancedGlobalSecondaryIn
         return EnhancedGlobalSecondaryIndex.builder()
                                            .indexName(indexMetadata.name())
                                            .projection(pb -> pb.projectionType(ProjectionType.ALL))
-                                           .provisionedThroughput(ptb -> ptb.readCapacityUnits(20L).writeCapacityUnits(20L))
                                            .build();
     }