remove unused spotbugs configuration

The configuration for the SpotBugs engine currently picked up `com.github.spotbugs:spotbugs:4.7.3`,
in spite of our attempt to explicitly configure `com.github.spotbugs:spotbugs:4.5.2`,
see `gradlew dependencies --configuration spotbugs`.

Signed-off-by: Manfred Hanke <Manfred.Hanke@tngtech.com>

buildSrc/src/main/groovy/archunit.java-code-quality-conventions.gradle

@@ -3,13 +3,7 @@ plugins {
     id 'com.diffplug.spotless'
 }
 
-dependencies {
-    spotbugs "com.github.spotbugs:spotbugs:${spotbugs.toolVersion.get()}"
-}
-
 spotbugs {
-    toolVersion = '4.5.2'
-
     excludeFilter = rootProject.file('buildSrc/src/main/resources/code_quality/spotbugs-excludes.xml')
 }