Debian images no longer ship DWARF debugging symbols

[malor]

Since #687, the regular Debian images no longer ship DWARF symbols, which heavily limits the ability to use gdb and lldb for debugging.

Stripping debugging symbols makes perfect sense to reduce the size of Docker images, but when this optimization was first introduced in #483, the idea was to restrict its use to the slim and Alpine images. That was (unintentionally?) changed in #483, and now debugging symbols are also stripped in the regular Debian images.

WDYT about restoring the previous behavior and limiting this optimization to the slim and Alpine images? (#693).