Do not depend on Shadow plugin in subprojects

Since buildSrc depends on the Shadow plugin, it's already in the
classpath of all build scripts

libraries/reflect/build.gradle.kts

@@ -17,7 +17,6 @@ buildscript {
     }
     dependencies {
         classpath("net.sf.proguard:proguard-gradle:${property("versions.proguard")}")
-        classpath("com.github.jengelman.gradle.plugins:shadow:${property("versions.shadow")}")
     }
 }