meson.build: Fix warning for configure_file

We claim to support meson versions >= 0.47 but the `install:` argument
in configure_file was introduced in version 0.50. This produces the
following meson warning:

WARNING: Project specifies a minimum meson_version '>= 0.47' but uses
features which were added in newer versions:
 * 0.50.0: {'install arg in configure_file'}

From the documentation for the install argument [1]:
" When omitted it (install) defaults to true when install_dir is set and
not empty, false otherwise."

So, remove the `install:` argument and just depend on `install_dir` for
installing.

Fixes: wayland/weston#225

[1] https://mesonbuild.com/Reference-manual.html#configure_file



Signed-off-by: Harish Krupo <harish.krupo.kps@intel.com>
(cherry picked from commit b81fc517)