Remove unnecessary inline

[jmcarcell]

BEGINRELEASENOTES

• Remove unnecessary inline in std_interoperability.cpp since the variables are only used in that file.
  ENDRELEASENOTES

[m-fila]

A constexpr specifier used in an object declaration or non-static member function(until C++14) implies const. A constexpr specifier used in a function or static data member(since C++17) declaration implies inline.

Those are variable declarations so inline isn't implied. Same in key4hep/k4FWCore/pull/248. Was this marked by some linter?

[tmadlener]

I agree with @m-fila here. On the other hand it shouldn't matter too much in this case since we are not relying on anything that would require them to be inline (i.e. we are not explicitly linking against any of this code, nor are we expecting the variables to have the same address in all translation units).

[jmcarcell]

Yeah inline is not doing anything here, the same object code is produced with and without so it may as well be removed. I'll change the title.