build: remove workarounds for unsupported gettext versions

build: remove workarounds for unsupported gettext versions

Now that we depend on gettext >= 0.19.2 remove the workaround
for issues in autopoint 0.18.3.  Note the scheme currently used in
newer gettext (autopoint) to avoid these issues requires
autoconf >= 2.69, therefore we update this requirement also.

Note the gettext version dependence from gnulib comes from
gnulib using gettext macros, and coreutils indirectly depends on
the gettext module due to:
http://git.sv.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=41dca647
bootstrap will then update m4/po.m4 and thus require a
supportng gettext version.

* bootstrap: Remove moot warning (resyncing with gnulib).
* configure.ac (AC_PREREQ): Change to 2.69 (now 3 years old).