i18n: Stop adding location comments to po files

Each time the po files are regenerated xgettext adds location
information for each translation string.  Given our method of feeding
xgettext from stdin, this information is useless.  By passing
--no-location to the invocation of xgettext we will suppress the extra
output.  Once applied, future i18n patches will not introduce so much
noise and it will be easier to see what was actually changed.

Signed-off-by: Adam Litke <agl@linux.vnet.ibm.com>
Reviewed-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>