Revert "package/meson: bump version to 0.50.0"

Revert "package/meson: bump version to 0.50.0"

This reverts commit 114e9dcd28e1001b74689215ec669b8940dc3ea9.
Indeed, there is major issue with this version because c_std is not
passed anymore when cross-compiling:
https://github.com/mesonbuild/meson/issues/5097

As a result, some meson packages (at least systemd, libmpdclient,
glib-networking) fail to build

Fixes:
 - http://autobuild.buildroot.org/results/9eae2181fb3fcfe12481e5496b7d87c0dcd109eb
 - http://autobuild.buildroot.org/results/e828c7925d9247e14d8a8694febfee8ce6c86e81
 - http://autobuild.buildroot.org/results/031aee7cf12ad882727eb2da5e953fd8813b52e2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>