configure*: remove extraneous blank lines (warning)

Added on commit d1acb31c9 ("compile time: enable LTS", 2021-02-28).

Note: Do not print a preceding blank line because one is already printed
right before the warning message, right after the items on "Features:".

Example of the resulting warning message:

    $ autoconf && ./configure
    [...]
    configure: creating ./config.status
    config.status: creating config.mk
    config.status: creating config.sh

    Compile options:
       [...]
       prefix: /usr/local
       sysconfdir: ${prefix}/etc
       Spectre compiler patch: yes

    Features:
       [...]
       SELinux labeling support:
       user namespace: -DHAVE_USERNS
       X11 sandboxing support: -DHAVE_X11

    *********************************************************
    *    Warning: Long-term support (LTS) was enabled!      *
    *    Most compile-time options have been rewritten!     *
    *********************************************************

    $

1 files changed, 0 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index 0fe34d6af..a78688e09 100644
--- a/configure.ac
+++ b/configure.ac
@@ -322,13 +322,10 @@ EOF
 
 if test "$HAVE_LTS" = -DHAVE_LTS; then
         cat <<\EOF
-
-
 *********************************************************
 *    Warning: Long-term support (LTS) was enabled!      *
 *    Most compile-time options have been rewritten!     *
 *********************************************************
 
-
 EOF
 fi