Now that autotools is gone and you always build to a dedicated build
directory with meson, we can remove .gitignore files that only had the
purpose of ignoring built binaries in the source directories.

Signed-off-by: Petri Latvala <petri.latvala@intel.com>
Cc: Arkadiusz Hiler <arek@hiler.eu>
Reviewed-by: Arkadiusz Hiler <arek@hiler.eu>