Fix libselinux => liblog dependencies

LOG_EVENT_STRING is not defined for liblog.vendor. Don't use it
for libselinux_vendor.

Test: mma -j
Test: BOARD_VNDK_VERSION=current mma -j

Bug: 63034227
Change-Id: Ibb653dac74da1ad678ccd5fabba97ab9bd0f0c38
(cherry picked from commit 09dff7c3a513e6043f2c089401e5f06d8e2fb9d6)
1 file changed