[compiler] Deprecate tf2tfliteV2, one-cmds 'converter_version'

[seanshpark]

As we can only use v2, it is not necessary accept converter_version.
Let's deprecated this option.
Removing this option may cause problems to the users, so leave this for some time (a year?)

[seanshpark]

• from [compiler] TF import set default to v2 #15735

[seanshpark]

now converter_version=... is ignored,
and --v1 or --v2 will show depreated message.