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/a0.c

@@ -4,7 +4,7 @@ TEST_BEGIN(test_a0) {
 	void *p;
 
 	p = a0malloc(1);
-	assert_ptr_not_null(p, "Unexpected a0malloc() error");
+	expect_ptr_not_null(p, "Unexpected a0malloc() error");
 	a0dalloc(p);
 }
 TEST_END