Update `SpringBootConfigurationFactory` so that it no longer attempts
to get a `LoggingSystem`.
The recent `LoggingSystem` update means makes use of the
`SpringFactoriesLoader` class to load candidate logging systems.
Unfortunately, the `SpringFactoriesLoader` class creates a `Logger`
which (when using Log4J2) causes `SpringBootConfigurationFactory` to
run. Calling `LoggingSystem.get` from `SpringBootConfigurationFactory`
results in a recursive call to `SpringFactoriesLoader` which hasn't
yet been fully initialized. We then see an NPE caused by a `null`
`cache`.
This update removes the call to `LoggingSystem.get` with the assumption
that it would never return `null` anyway.
Fixes gh-24163
0ce3e7ec6b