build(gradle): Do not set a global duplicatesStrategy anymore

This effectively reverts 2086f72 which was just added as a work-around
for the bug of IntelliJ IDEA adding multiple `classpath.index` files
which by now has been fixed.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

buildSrc/src/main/kotlin/ort-base-conventions.gradle.kts

@@ -43,7 +43,6 @@ repositories {
 }
 
 tasks.withType<AbstractArchiveTask>().configureEach {
-    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
     isPreserveFileTimestamps = false
     isReproducibleFileOrder = true
 }