This reverts commit b2bc934e21.
The commit does causes issues when a user manually removes channels:
The disk-reader's ::can_support_io_configuration() at first ignores
the user's request, forcing the output channel count to match the
DR's current channel config.
However, when configuring the DiskReader after that, channels is updated
to match the new input-count.
Even though the DR itself only plays back using the confgured I/O,
all processors after it still use the old channel count.
Only a later, second re-configuration step will apply the actual removal
to plugins and port.
PS. the original commit was mainly intended to fix a crash when
adding an instrument plugin *between* disk-writer and disk-reader
on a MIDI track.
Robin Gareus
c8f1146124
