ld/doc: Remove '.info' suffix in @ref, etc

Texinfo 7.2 began showing warnings like:

    ld.texi:1026: warning: do not set .info suffix in reference for manual `gcc.info'
    ld.texi:9689: warning: do not set .info suffix in reference for manual `binutils.info'

The Texinfo developers plan to stop removing the '.info' suffix
internally in a future release so without this patch the references will
break in the future.

Signed-off-by: Collin Funk <collin.funk1@gmail.com>