Do not preserveAspectRatio for terminate-block.

[HansOlsson]

The reason is that you want to write an expression and it is natural to adapt the length of the block to the expression, which will give different aspect ratios. This is consistent with the source-block BooleanExpression. Related to #3985

[HansOlsson]

Note that:

• The block is used in two places in MSL: Modelica.Mechanics.MultiBody.Examples.Systems.RobotR3.Utilities.PathPlanning1 (and 6). Neither of them have the given aspect ratio, - this is a clear indication that preserving the aspect ratio doesn't give the desired result.
• If the aspect ratio isn't preserved the square in the terminate-symbol will no longer be square (as seen in those models), however, the benefit of more readable text outweighs the minor non-squareness.

[TManikantan]

@AHaumer and @MartinOtter would you please review fix for this ticket? Please also let us know if additional info or summary would help you expedite the review.