Prevent the BrightLineFalsingManager from duping its session.

The BrightLineFalsingManager should not be able to start a session
when it's already in a session. Primarily, this caused the
FalsingManager to hang onto extra registrations to the Proximity
Sensor, per the bug.

Bug: 138220274
Test: atest SystemUITests and manual.
Change-Id: Id10d2697a96524e98c87aaa87702209d1752fe68
(cherry picked from commit 0ae8f2e36a6c86d54585fd57d55e184b0d99de1c)
diff --git a/packages/SystemUI/src/com/android/systemui/classifier/brightline/BrightLineFalsingManager.java b/packages/SystemUI/src/com/android/systemui/classifier/brightline/BrightLineFalsingManager.java
index 3d869bc..6280c9f 100644
--- a/packages/SystemUI/src/com/android/systemui/classifier/brightline/BrightLineFalsingManager.java
+++ b/packages/SystemUI/src/com/android/systemui/classifier/brightline/BrightLineFalsingManager.java
@@ -98,10 +98,12 @@
     }
 
     private void sessionStart() {
-        logDebug("Starting Session");
-        mSessionStarted = true;
-        registerSensors();
-        mClassifiers.forEach(FalsingClassifier::onSessionStarted);
+        if (!mSessionStarted) {
+            logDebug("Starting Session");
+            mSessionStarted = true;
+            registerSensors();
+            mClassifiers.forEach(FalsingClassifier::onSessionStarted);
+        }
     }
 
     private void sessionEnd() {