Doc fix.

INSTALL.rst

@@ -16,17 +16,6 @@ of m4 macros. If you encounter difficulties in the ``configure`` step,
 make sure that you have the archive installed (typically as the
 package ``autoconf-archive`` on many distributions).
 
-To configure the build for libgcrypt, ``configure.ac`` uses the macro
-``AM_PATH_LIBGCRYPT`` from the Autoconf Archive, which in turn invokes
-the ``libgcrypt-config`` utility. The macro specifies a minimum
-library and API version number that is required, currently libgcrypt
-version 1.6.3 and API version 1. If you want to build against a
-version of libgcrypt at a non-standard location (that is, whose path
-that differs from the one described by ``libgcrypt-config``), then use
-the ``configure`` option
-``--with-libgcrypt-prefix=$LIBGCRYPT_PREFIX``, where
-``$LIBGCRYPT_PREFIX`` is the alternative path.
-
 The ``make check`` step requires that the VMOD blobcode is installed
 for the Varnish instance against which the build is executed.