Using the identity \( \cos (90^\circ - x) = \sin x \), we simplify the expression:
\[
\cos 70^\circ = \sin 20^\circ \quad \text{and} \quad \sin 70^\circ = \cos 20^\circ
\]
Substituting these values into the expression:
\[
\frac{\cos 20^\circ \cos 70^\circ - \sin 20^\circ}{\sin 70^\circ} = \frac{\cos 20^\circ \sin 20^\circ - \sin 20^\circ}{\cos 20^\circ}
\]
Factor out \( \sin 20^\circ \):
\[
\frac{\sin 20^\circ (\cos 20^\circ - 1)}{\cos 20^\circ}
\]
Since \( \cos 20^\circ - 1 = 0 \), the entire expression simplifies to:
\[
0
\]
Thus, the correct answer is 0.