AMS: stop checking for CryptKeeper mode before setting dev.bootcomplete

Since support for Full Disk Encryption was removed in favor of
File Based Encryption, "CryptKeeper mode" no longer exists and the
"vold.decrypt" and "vold.encrypt_progress" properties are never set.
Therefore, remove the unnecessary check for CryptKeeper mode from
ActivityManagerService::finishBooting().

Bug: 208476087
Change-Id: I1c7cb8a2dec67dda9b673de8a811229a82fee482