Revert "dock:: read theme icon from /etc/deepin-version"

This reverts commit ff8f361e58d8eb9f953590b010c6fe92fc3805eb.

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/e95ad265026843e5a8ff7d840a9c7816/

Change-Id: Ibf2d547213fe45eaba4691510ec485cba02d19ff