README: remove PREFERRED_VERSION from instructions
README: remove PREFERRED_VERSION from instructions

Due to the fact that currently only one openjdk-7-jre and
icedtea7-native version is included in meta-java, their PREFERRED_VERSION
selections are removed from the usage instructions in the README file.

Signed-off-by: Richard Leitner <0f2fdd4d2dfbb4dde6236fd550af0a2071b34781@skidata.com>
Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

rehsack/meta-java,tobw/meta-java,tobw/meta-java,rehsack/meta-java,rehsack/meta-java,rehsack/meta-java,rdm-dev/meta-java,tobw/meta-java,rdm-dev/meta-java,rehsack/meta-java,rdm-dev/meta-java