Fix fmi-ls-bus header description section

ls-bus-guide/4____network_abstraction.adoc

@@ -9,18 +9,13 @@ This section shows the exemplary implementation in conjunction with the provided
 
 ===== Provided Header Files [[low-cut-can-getting-started-provided-header-files]]
 Besides the textual specification for FMUs with bus support, the Layered Standard for Network Communication also provides a C API to make the creation of FMUs with bus support as easy and generalized as possible.
-The standard differentiates between two groups of files within the C API: Mandatory and optional files.
 
 * https://github.com/modelica/fmi-ls-bus/blob/main/headers/fmi3LsBus.h[fmi3LsBus.h] provides general macros, types and structures of common Bus Operations.
 This header file applies to all supported bus types of the layered standard.
-The usage of this file is mandatory.
 * https://github.com/modelica/fmi-ls-bus/blob/main/headers/fmi3LsBusCan.h[fmi3LsBusCan.h] provides macros, types and structures of Bus Operations explicit for CAN, CAN FD and CAN XL.
 Primarily, structures are included here that allow the Bus Operations specified by the layered standard to be easily created and used.
-The usage of this file is mandatory.
 * https://github.com/modelica/fmi-ls-bus/blob/main/headers/fmi3LsBusUtil.h[fmi3LsBusUtil.h] provides common utility macros and structures for all supported bus types.
-The usage of this file is optional.
 * https://github.com/modelica/fmi-ls-bus/blob/main/headers/fmi3LsBusUtilCan.h[fmi3LsBusUtilCan.h] provides CAN, CAN FD and CAN XL explicit utility macros.
-The usage of this file is optional.
 
 ===== General Aspects
 Bus Operations represent protocol units to be transmitted in the environment of the layered standard based on the https://modelica.github.io/fmi-ls-bus/main/#low-cut-layered-standard-bus-protocol[Layered Standard Bus Protocol].