Fix logback.xml warnings

[paul-butcher]

When attempting to diagnose a recent problem, I was doing a bit of logmining and stumbled across these three warnings (and an INFO with a message that looks rather WARNING-ish)

16:50:37,518 |-WARN in ch.qos.logback.classic.LoggerContext[default] - Resource [logback.xml] occurs multiple times on the classpath.
16:50:37,518 |-WARN in ch.qos.logback.classic.LoggerContext[default] - Resource [logback.xml] occurs at [jar:file:/opt/docker/lib/weco.storage_2.12-32.13.0.jar!/logback.xml]
16:50:37,518 |-WARN in ch.qos.logback.classic.LoggerContext[default] - Resource [logback.xml] occurs at [jar:file:/opt/docker/lib/weco.id_minter-6368.8175ff3359d989339bf9ed1957f7a587193a2241.jar!/logback.xml]
16:50:37,554 |-INFO in ch.qos.logback.core.joran.spi.ConfigurationWatchList@4c15e7fd - URL [jar:file:/opt/docker/lib/weco.id_minter-6368.8175ff3359d989339bf9ed1957f7a587193a2241.jar!/logback.xml] is not of type file

If we can get rid of them, it would make the logs a bit cleaner, so that real problems are easier to find.

(It's not just four log entries, this quatrain appears several times during a reindex)