We have open review for metal pipeline implementation : https://github.com/openjdk/jdk/pull/2403

This bug handles review comments :
Removing incorrent maxNativetextureSize comment : https://github.com/openjdk/jdk/pull/2403#discussion_r571214582
Removes import in CGraphicsConfig.java : https://github.com/openjdk/jdk/pull/2403#discussion_r572199603
Removes OpenGL comments in MTLContext : https://github.com/openjdk/jdk/pull/2403#discussion_r572229444 , https://github.com/openjdk/jdk/pull/2403#discussion_r572229652