[Regression] Beam_collision_engraver and StaffSymbol overrides

[Bertrand Bordage]

Hello,

When we use a smaller staff, Beam_collision_engraver creates collisions that
where not in 2.12.

\version "2.13"
music = << \relative c'' { e16 f e c } \\ \relative c''' { g a g e } >>

\new Staff \music
\new Staff \with {
  fontSize = #-3
  \override StaffSymbol #'staff-space = #(magstep -3)
  \override StaffSymbol #'thickness = #(magstep -3) }
  \music

In this simple case, removing Beam_collision_engraver on the small staff
solves the problem. But on more complicated cases, Beam_collision_engraver
should handle this.
Or, at least for the moment, we should add "\remove Beam_collision_engraver"
to the ossia staves doc (NR 1.6.2).

Regards,
Bertrand