Fix theme for PostCallActivity

NoActionBar theme is more proper for PostCallActivity since no need any
title and a send button can have a vivid color when enabled.

Test: am start -n com.android.dialer/.postcall.PostCallActivity -e
"phone_number" "12345678"

Signed-off-by: Sungjae <sung_jae.kim@samsung.com>
Change-Id: I1971f5b2db2674f298f3f442f0113309d5523a7c