Get rid of the `heapG` dependency on `lty`.

1 job for master in 11 minutes (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #24276
fp
build-iris.dev

00:11:00

 
Name Stage Failure
failed
build-iris.dev Build
Makefile.coq:317: recipe for target 'all' failed
make[1]: *** [all] Error 2
Makefile:6: recipe for target 'all' failed
make: *** [all] Error 2

real 5m42.715s
user 28m19.924s
sys 0m40.348s
ERROR: Job failed: exit code 1