configure.ac: drop redundant AC_SUBSTs and content-free comments
configure.ac: drop redundant AC_SUBSTs and content-free comments

Signed-off-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>
Reviewed-by: Xavier Claessens <6f61b6f8ca6f7cbeae6bb087ddf85cf85dce43eb@collabora.co.uk>

freedesktop-unofficial-mirror/telepathy__telepathy-idle,freedesktop-unofficial-mirror/telepathy__telepathy-idle,freedesktop-unofficial-mirror/telepathy__telepathy-idle