Take a look at JCE's DIY article about stereo installation in the 124's. I think he covers the removal of that panel as well.
On the 126 I had to carefully pry that panel down a tad to pop it out after the ashtray and stereo were removed. Once pried down it just sort of popped out enough to pull it from the dash and disconnect the plugs on the back of the switches. Be careful of the optic light cables that run to several of the switches.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.