remove the command to download prepared test Dash files. user need to prpare it by themselves

Author: hzhan80

src/external/run_test.sh

@@ -14,7 +14,7 @@ cd -
 # OmafDashAccess test
 ################################
 cd OmafDashAccess
-curl -H 'X-JFrog-Art-Api: AKCp5dL3Kxmp2PhDfYhT2oFk4SDxJji5H8S38oAqmMSkiD46Ho8uCA282aJJhM9ZqCKLb64bw' -O "https://ubit-artifactory-sh.intel.com/artifactory/immersive_media-sh-local/testfile/segs_for_readertest_0909.tar.gz" && tar zxf segs_for_readertest_0909.tar.gz
+# please prepare dash segments for test
 
 ./testMediaSource --gtest_filter=*_static
 ./testMediaSource --gtest_filter=*_live