Use system protobuf-java - copied into dependencies/flatRepo

Index: gradle.properties
--- gradle.properties.orig
+++ gradle.properties
@@ -6,4 +6,4 @@ org.gradle.jvmargs=-Xmx2G -Duser.language=en -Duser.co
 org.gradle.archives.use-file-system-permissions=true
 
 # Set Ghidra protobuf version
-ghidra.protobuf.java.version=4.31.0
+ghidra.protobuf.java.version=${PROTOBUF_JAVA_VER}
