Plugin: Remove obsolete comments about "nexes" attribute. Clarify how "src" and "nacl" attributes in <embed> affect __nacl and __src properties on the plugin.
Plugin: Remove obsolete comments about "nexes" attribute. Clarify how "src" and "nacl" attributes in <embed> affect __nacl and __src properties on the plugin.

Note that "src" will be going away at some point, but in the meantime the behavior of these attributes in tests has been causing confusion.

BUG=none
TEST=bots
Review URL: http://codereview.chromium.org/6811035

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4813 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client