Remove deprecated isReadDataAvailable

[MakisH]

As discussed in precice/precice#1223, preCICE v2.5.0 deprecated isReadDataAvailable(), which is planned for removal in preCICE v3. Related: #235.

This PR already removes this call, to avoid the deprecation warning when compiling the adapter.

It should currently not matter for results, as it re-reads the same information on the boundary, but it should make time interpolation easier in the future. I quickly ran the flow-over-heated-plate case with subcycling (2 solver time steps for 1 coupling time window) and implicit coupling (hint: we currently have issues with FSI and subcycling #58), and the result files are identical. In this small case, the runtime seems to be approximately the same (without any rigorous performance test, just one sample for each case).

Still, the adapter performs now each assignment on the boundaries every time.

@uekerman / @davidscn Anything else to consider here?

The diff may look a bit complicated, but it is just removing one if check and indenting-out.

TODO list:

• I updated the documentation in docs/
• I added a changelog entry in changelog-entries/ (create directory if missing)

[davidscn]

Looks good

[thesamriel]

Using serial coupling, participant 1 reads all quantities from a zero buffer before the first timestep. This sets the boundary values at the interface to 0 for all read variables, correct?

This becomes problematic when using compressible flows in fluid-fluid coupling, since a 0 pressure leads to a division by 0 error.

Ran into this problem for my flow over heated wall segment test case for fluid-fluid coupling after updating the adapter.

[MakisH]

This sounds like a data initialization issue to me, which should be documented independently.

The purpose of the isReadDataAvailable was mostly to not read again and again when subcycling.