Revert "Add APK container signing key/cert pairs for APEXes"

This reverts commit 74f27716.

The key/cert pairs for APEXes are moved to the same directory where the
APEXes are defined.

Test: Check this for all APEXes
jarsigner -verify -verbose -certs out/target/product/blueline/system/apex/com.android.tzdata.apex shows
...
X.509, CN=com.android.tzdata, OU=Android, O=Android, L=Mountain View, ST=California, C=US

Change-Id: I8d867b434b93aa68cbc707fa20ed8dbd4cef755e