RELEASES.md: clarify what to do about files required by Fiji
RELEASES.md: clarify what to do about files required by Fiji

... when they will be marked as obsolete on the ImageJ site...

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

TehSAUCE/imagej,biovoxxel/imagej,biovoxxel/imagej,biovoxxel/imagej,TehSAUCE/imagej,TehSAUCE/imagej