Remove trailing 'extractive' word from en documentation (#21594)

remove trailing word

docs/source/en/task_summary.mdx

@@ -217,7 +217,7 @@ Question answering is another token-level task that returns an answer to a quest
 
 There are two common types of question answering:
 
-* extractive: extractive: given a question and some context, the answer is a span of text from the context the model must extract
+* extractive: given a question and some context, the answer is a span of text from the context the model must extract
 * abstractive: given a question and some context, the answer is generated from the context; this approach is handled by the [`Text2TextGenerationPipeline`] instead of the [`QuestionAnsweringPipeline`] shown below