Move otacerts module from Android.mk to Android.bp

Remove the otacerts module defined in Android.mk. Instead, provide
variables to soong.

Bug: 335364209
Test: Define "PRODUCT_DEFAULT_DEV_CERTIFICATE := \
                 build/make/target/product/security/testkey" and
      m aosp_cf_system_x86_64
Change-Id: I99a484e04984da8bd7f58deecd90c880de16fd71