fix "make dist" ready for 8.13 rc1

libvips/foreign/libnsgif/update.sh

@@ -18,8 +18,7 @@ cp libnsgif/src/gif.c .
 cp libnsgif/test/cli.[ch] test/
 cp libnsgif/test/nsgif.c test/
 
-if [ -d "patches" ]
-then
+if [ -d patches ]; then
   echo applying patches ...
   for patch in patches/*.patch; do
     patch -p0 <$patch

po/POTFILES.in

@@ -287,9 +287,6 @@ libvips/foreign/vipssave.c
 libvips/foreign/webp2vips.c
 libvips/foreign/webpload.c
 libvips/foreign/webpsave.c
-libvips/foreign/libnsgif/libnsgif.c
-libvips/foreign/libnsgif/lzw.c
-libvips/foreign/libnsgif/test/decode_gif.c
 libvips/freqfilt/freqfilt.c
 libvips/freqfilt/freqmult.c
 libvips/freqfilt/fwfft.c