Remove no-longer-necessary GCOVR_EXCL_LINE

Now that we exclude noncode lines (why isn't that the default?)

ConflictSet.cpp

@@ -2539,7 +2539,7 @@ Vector<uint8_t> getSearchPath(Arena &arena, Node *n) {
   }
   std::reverse(result.begin(), result.end());
   return result;
-} // GCOVR_EXCL_LINE
+}
 
 // Return true if the max version among all keys that start with key + [child],
 // where begin < child < end, is <= readVersion.