generate: NewFromSpec() remove deprecated comment
generate: NewFromSpec() remove deprecated comment

The recommended replacement does not work because other code paths expect
an initialized envCacheMap.

Fixes #720

Signed-off-by: Paul Holzinger <f1d90b51f8389bff6167e11781e462f44a71d746@redhat.com>

opencontainers/runtime-tools,opencontainers/runtime-tools