Make imports private where possible

Co-authored-by: Anders Schack-Mulligen <aschackmull@users.noreply.github.com>

Author: smowton

java/ql/src/semmle/code/java/frameworks/google/GoogleHttpClientApi.qll

@@ -1,7 +1,7 @@
 import java
 import semmle.code.java.Serializability
 import semmle.code.java.dataflow.DataFlow
-import semmle.code.java.dataflow.internal.DataFlowForSerializability
+private import semmle.code.java.dataflow.internal.DataFlowForSerializability
 
 /** The method `parseAs` in `com.google.api.client.http.HttpResponse`. */
 private class ParseAsMethod extends Method {

java/ql/src/semmle/code/java/frameworks/jackson/JacksonSerializability.qll

@@ -7,7 +7,7 @@ import java
 import semmle.code.java.Serializability
 import semmle.code.java.Reflection
 import semmle.code.java.dataflow.DataFlow
-import semmle.code.java.dataflow.internal.DataFlowForSerializability
+private import semmle.code.java.dataflow.internal.DataFlowForSerializability
 import semmle.code.java.dataflow.FlowSteps
 private import semmle.code.java.dataflow.ExternalFlow