Amputate[exp, q1, q2, ...] amputates Eps and DiracGamma. Amputate[exp,q1,q2,Pair->{p}] amputates also p.q1 and p.q2; Pair->All amputates all except OPEDelta.
Overview, DiracGamma, GA, DiracSimplify, GS, DiracTrick.
GS[p] . GS[q]\left(\bar{\gamma }\cdot \overline{p}\right).\left(\bar{\gamma }\cdot \overline{q}\right)
Amputate[%, q]q^{\text{\$AL\$16479}(1)} \left(\bar{\gamma }\cdot \overline{p}\right).\gamma ^{\text{\$AL\$16479}(1)}