package/m4: remove --disable-static for host package

This issue was reported by Firas Khalil Khana on a Github pull request
at https://github.com/buildroot/buildroot/pull/113/.

There is no --disable-static in m4. Research in the dark corners of
the Git history has shown that it was apparently added by Peter
Korsgaard back in 2009, in commit
3467cf7305 ("m4: cleanup"). At this
time, the version of m4 used was 1.4.9, but even looking at the
tarball of this old release shows that the ./configure did not support
--disable-static.

So let's drop this option.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/m4/m4.mk

@@ -9,6 +9,5 @@ M4_SOURCE = m4-$(M4_VERSION).tar.xz
 M4_SITE = $(BR2_GNU_MIRROR)/m4
 M4_LICENSE = GPL-3.0+
 M4_LICENSE_FILES = COPYING
-HOST_M4_CONF_OPTS = --disable-static
 
 $(eval $(host-autotools-package))