Redundant of removed.

Author: Karsten7

source/reference/operator/aggregation/toDouble.txt

@@ -21,7 +21,7 @@ Definition
 
    .. versionadded:: 4.0
 
-   Converts a value of to a double. If the value cannot be converted to
+   Converts a value to a double. If the value cannot be converted to
    an double, :expression:`$toDouble` errors. If the value is null or
    missing, :expression:`$toDouble` returns null.