Remove unused doc reference URL

Author: cjbj

doc/api.md

@@ -19000,7 +19000,6 @@ can be asked at [AskTom][158].
 [180]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-35CB2592-7588-4C2D-9075-6F639F25425E
 [181]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-A9D4A5F5-B939-48FF-80AE-0228E7314C7D
 [182]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-E63D75A1-FCAA-4A54-A3D2-B068442CE766
-[183]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=RACAD
 [184]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-805AB986-DE12-4FEA-AF56-5AABCD2132DF
 [185]: https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-F20C5DC5-C2FC-4145-9E4E-345CCB8148C7
 [186]: https://static.rainfocus.com/oracle/oow19/sess/1553616880266001WLIh/PF/OOW19_Net_CON4641_1569022126580001esUl.pdf