Remove redundant import

Author: smowton

java/ql/lib/semmle/code/java/deadcode/DeadField.qll

@@ -3,7 +3,6 @@ import semmle.code.java.deadcode.DeadCode
 import semmle.code.java.frameworks.javaee.Persistence
 import semmle.code.java.frameworks.JAXB
 import semmle.code.java.frameworks.jackson.JacksonSerializability
-import semmle.code.java.frameworks.javaee.Persistence
 
 /**
  * A field that is from a source file.