Change tzdatacheck to avoid hardcoding

Motivation: Remove hardcoding from tzdatacheck
and reduce futre risk of /system binary and format
version falling out of step on a device.

Switch from hardcoding format version information in
tzdatacheck.cpp to using the tz_version file instead.
A future change will track the movement of tz_version
from /system to inside /apex/com.android.runtime.

tzdatacheck will likely go away in an upcoming release but
it will be kept working for now.

tz_version also contains rules version information so
tzdatacheck does not need to read the tzdata file's header
any more.

README.android has also been updated to reflect this and other
recent changes.

Bug: 119851164
Test: run cts -m CtsHostTzDataTests
Change-Id: I752450b4f730a03a9dc3a39e30179f00229c9e0c