Remove unnecessary public getFromStack method

The getFromStack() method was made public with @VisibleForTesting but
was never actually used in our tests or implementation. The CallStack.size()
method is the one that's actually needed and used via getCurrentPathStack().size().

This keeps the API surface minimal and only exposes what's necessary.

Author: maple-buice

src/main/java/com/hubspot/jinjava/interpret/Context.java

@@ -17,7 +17,6 @@
 package com.hubspot.jinjava.interpret;
 
 import com.google.common.annotations.Beta;
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.SetMultimap;
@@ -682,8 +681,7 @@ public CallStack getIncludePathStack() {
     return includePathStack;
   }
 
-  @VisibleForTesting
-  public CallStack getFromStack() {
+  private CallStack getFromStack() {
     return fromStack;
   }