Python: Cleanup "first" type-tracking predicate to be private

Since it's exposed nicely in the version that doesn't have a
`DataFlow::TypeTracker` parameter, these should be private.

Also found one instance where I had accidentially used DataFlow::Node instead of
LocalSourceNode

python/ql/src/semmle/python/Concepts.qll

@@ -563,7 +563,9 @@ module Cryptography {
     /** Provides classes for modeling new key-pair generation APIs. */
     module KeyGeneration {
       /** Gets a back-reference to the keysize argument `arg` that was used to generate a new key-pair. */
-      DataFlow::LocalSourceNode keysizeBacktracker(DataFlow::TypeBackTracker t, DataFlow::Node arg) {
+      private DataFlow::LocalSourceNode keysizeBacktracker(
+        DataFlow::TypeBackTracker t, DataFlow::Node arg
+      ) {
         t.start() and
         arg = any(KeyGeneration::Range r).getKeySizeArg() and
         result = arg.getALocalSource()

python/ql/src/semmle/python/dataflow/new/TypeTracker.qll

@@ -180,7 +180,7 @@ private newtype TTypeTracker = MkTypeTracker(Boolean hasCall, OptionalAttributeN
  * It is recommended that all uses of this type are written in the following form,
  * for tracking some type `myType`:
  * ```
- * DataFlow::LocalSourceNode myType(DataFlow::TypeTracker t) {
+ * private DataFlow::LocalSourceNode myType(DataFlow::TypeTracker t) {
  *   t.start() and
  *   result = < source of myType >
  *   or
@@ -341,7 +341,7 @@ private newtype TTypeBackTracker = MkTypeBackTracker(Boolean hasReturn, Optional
  * for back-tracking some callback type `myCallback`:
  *
  * ```
- * DataFlow::LocalSourceNode myCallback(DataFlow::TypeBackTracker t) {
+ * private DataFlow::LocalSourceNode myCallback(DataFlow::TypeBackTracker t) {
  *   t.start() and
  *   result = (< some API call >).getArgument(< n >).getALocalSource()
  *   or

python/ql/src/semmle/python/frameworks/Cryptography.qll

@@ -76,7 +76,7 @@ private module CryptographyModel {
     }
 
     /** Gets a reference to a predefined curve class instance with a specific key size (in bits), as well as the origin of the class. */
-    private DataFlow::Node curveClassInstanceWithKeySize(
+    private DataFlow::LocalSourceNode curveClassInstanceWithKeySize(
       DataFlow::TypeTracker t, int keySize, DataFlow::Node origin
     ) {
       t.start() and