Include secilc and sepolicy conditionally, elsewhere

This removes the unconditional inclusion of secilc and sepolicy.
These artefacts are now conditionally included by system/core/init.
The reason for declaring the conditional inclusion there is because
the desired conditional inclusion based on PRODUCT_FULL_TREBLE cannot
be declared here because PRODUCT_FULL_TREBLE is not yet available when
this file is interpreted.

Test: Device boots, no additional SELinux denials. This test is
      performed on a device with PRODUCT_FULL_TREBLE set to true, and
      on a device with PRODUCT_FULL_TREBLE set to false.
Test: Device with PRODUCT_FULL_TREBLE set to true contains secilc and
      the three *.cil files, but does not contain the sepolicy file.
      Device with PRODUCT_FULL_TREBLE set to false contains sepolicy
      file but does not contain the secilc file or any *.cil files.
Bug: 31363362

Change-Id: Ia3f38948b71a054918f5f63c594ba62a033e1066