Change assert_* to expect_* in tests

```
grep -Irl assert_ test/ | xargs sed -i \
    's/witness_assert/witness_do_not_replace/g';
grep -Irl assert_ test/ | xargs sed -i \
    's/malloc_mutex_assert_owner/malloc_mutex_do_not_replace_owner/g';

grep -Ir assert_ test/ | grep -o "[_a-zA-Z]*assert_[_a-zA-Z]*" | \
    grep -v "^assert_"; # confirm no output
grep -Irl assert_ test/ | xargs sed -i 's/assert_/expect_/g';

grep -Irl witness_do_not_replace test/ | xargs sed -i \
    's/witness_do_not_replace/witness_assert/g';
grep -Irl malloc_mutex_do_not_replace_owner test/ | xargs sed -i \
    's/malloc_mutex_do_not_replace_owner/malloc_mutex_assert_owner/g';
```

test/unit/div.c

@@ -14,7 +14,7 @@ TEST_BEGIN(test_div_exhaustive) {
 		    dividend += divisor) {
 			size_t quotient = div_compute(
 			    &div_info, dividend);
-			assert_zu_eq(dividend, quotient * divisor,
+			expect_zu_eq(dividend, quotient * divisor,
 			    "With divisor = %zu, dividend = %zu, "
 			    "got quotient %zu", divisor, dividend, quotient);
 		}