klab-prove: stop passing custom tactic to z3

This could be a possible source of indeterminism, and we're anyway not
sure if we still need it.

Cf. discussion at #305.

libexec/klab-prove

@@ -132,7 +132,6 @@ timeout "$TIMEOUT" "$KLAB_EVMS_PATH/deps/k/k-distribution/target/release/k/bin/k
   --boundary-cells k,pc \
   --smt_prelude "$KLAB_OUT/prelude.smt2" \
   --concrete-rules "$(join_by , ${concrete_rules[@]})" \
-  --z3-tactic "(or-else (using-params smt :random-seed 3) (using-params smt :random-seed 2) (using-params smt :random-seed 1))" \
   "$target_spec" >"$STDOUT" 2>"$STDERR" & kprove_child=$!
 wait "$kprove_child"
 result=$?