[cleanup][style] Remove comment for header guard #endif

We sometimes add a comment to the header guards #endif like

#endif // DUMUX_COMMON_BLA

I think this is unnecessary clutter and should be removed.

• The last #endif in header files is always the header guard #endif
• When copying a header file to create a new header it is easy to forget to change this comment
• When changing the header guard it is easy to forget to change this comment