Optimize simplify_eq.

The case tactic is faster than destruct.
1 job for master in 1 minute and 29 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #1644
coq
buildjob

00:01:29

 
Name Stage Failure
failed
buildjob Test There is an unknown failure, please try again
make[1]: *** Waiting for unfinished jobs....
base_logic/upred (user: 1.82 mem: 460120 ko)
algebra/updates (user: 2.13 mem: 460188 ko)
algebra/local_updates (user: 2.94 mem: 461628 ko)
heap_lang/tactics (user: 4.55 mem: 486108 ko)
make[1]: Leaving directory '/builds/FP/iris-coq'
Makefile:13: recipe for target 'all' failed
make: *** [all] Error 2
ERROR: Build failed: exit code 1