docs(io): simplify DeleteFiles comments

Author: plusplusjiajia

src/iceberg/arrow/s3/arrow_s3_file_io.cc

@@ -284,9 +284,8 @@ Status ArrowS3FileIO::DeleteFile(const std::string& file_location) {
 }
 
 Status ArrowS3FileIO::DeleteFiles(const std::vector<std::string>& file_locations) {
-  // Like Java's S3FileIO, a failure neither stops the remaining deletes nor
-  // hides how many failed. One at a time costs nothing extra: Arrow's S3
-  // DeleteFiles deletes each file separately as well.
+  // Like Java's S3FileIO, keep going after a failure and report the count.
+  // Arrow's S3 DeleteFiles deletes one file at a time too.
   size_t failed = 0;
   for (const auto& file_location : file_locations) {
     if (auto status = FileIOForPath(file_location).DeleteFile(file_location);

src/iceberg/test/arrow_s3_file_io_test.cc

@@ -322,8 +322,7 @@ TEST_F(ArrowS3FileIOTest, DeleteFilesAttemptsEveryFile) {
     ASSERT_THAT(io->WriteFile(path, "payload"), IsOk());
   }
 
-  // Deletes under `denied` now authenticate with bad keys and fail; the one in
-  // between must still run.
+  // Deletes under `denied` fail; the one between them must still run.
   auto bad_properties = properties;
   for (const auto& [key, value] : BadS3Credentials()) {
     bad_properties.insert_or_assign(key, value);
@@ -334,8 +333,7 @@ TEST_F(ArrowS3FileIOTest, DeleteFilesAttemptsEveryFile) {
   EXPECT_THAT(io->DeleteFiles(paths), HasErrorMessage("Failed to delete 2 of 3 files"));
   EXPECT_FALSE(io->ReadFile(allowed, std::nullopt).has_value());
 
-  // With the default credentials back, the denied files must still exist:
-  // Arrow fails to delete a missing object.
+  // The denied files remain: Arrow fails to delete a missing object.
   ASSERT_THAT(credentialed->SetStorageCredentials({}), IsOk());
   EXPECT_THAT(io->DeleteFiles({paths[0], paths[2]}), IsOk());
 }