Remove unused mysql client
There is no instance on Mysql used in the current PB deployment of DefectDojo, and DefectDojo has not been tested with a hardened IB instance of Mysql, therefore it is not necessary to include the Mysql client binary in the image. The Mysql binary can always be added back in the future if anyone is using the IB DefectDojo image with Mysql, but for now it would just be extra software that would needed to be kept track of.