Exclude Spring Transaction from build - we don't need it

[andrewharmellaw]

You can see when we startup that Spring Transactions are being brought in.

20:27:00.823 [main] INFO o.s.c.s.PostProcessorRegistrationDelegate$BeanPostProcessorChecker - Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [class org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration$$EnhancerBySpringCGLIB$$407dba36] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

We don't use them by default so should exclude the dependency in build.gradle.