Remove debug info from release builds

[JonasWanke]

This reduces the release size from 177.4 MB to 14.2 MB for me and also speeds up compile times:

# time cargo build --release

# Before:
real    0m6,217s
user    0m32,679s
sys     0m1,407s

# After:
real    0m4,735s
user    0m22,096s
sys     0m0,528s

AFAIK, the debug info was only there for flamegraphs, but we can still enable it specifically for generating flamegraphs.

Checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)