init.rc: merge the zygote-start actions

The three actions for "zygote-start" are identical except for their
property triggers.  This seems to have been left over from when Android
supported both File Based Encryption (FBE) and Full Disk Encryption
(FDE), causing there to be four possible encryption states:

- ro.crypto.state=unsupported (No encryption configured)
- ro.crypto.state=encrypted && ro.crypto.type=file (FBE enabled)
- ro.crypto.state=unencrypted (FDE supported but disabled)
- ro.crypto.state=encrypted && ro.crypto.type=block (FDE enabled)

It seems that the reason the zygote-start action was duplicated three
times was to exclude the "FDE enabled" case, which could only be done by
explicitly listing the other three cases.

However, now that FDE is no longer supported, only the first two cases
are possible.  Therefore, zygote-start can just be the whole trigger.

Bug: 208476087
Test: presubmit
Change-Id: Icd6e4b0d2fb3f9f20595c0af4e2e35350564da8d