logd: remove SELinux dup handling

Remove the code which attempts to collapse multiple similar SELinux
denials into one denial. SELinux logs are already rate throttled by the
kernel
(https://android-review.googlesource.com/c/platform/system/core/+/941357
for example), so additional filtering here only adds complexity and may
result in SELinux denials being inappropriately suppressed or dropped.

Bug: 118815957
Test: atest logd-unit-tests
Change-Id: I611fa43dc56c99aa992aad002c16c742e6034e5c