[packages] cyrus-sasl: add config/libtool.m4 to PKG_REMOVE_FILES list (closes #11700)

Signed-off-by: Mark Baugher <mark@mbaugher.com>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@35483 3c298f89-4303-0410-b956-a3cf2f4a3e73