remove ImageIO dependency

This is for 1.0 backward compatibility

Author: johnnychen94

Project.toml

@@ -11,10 +11,9 @@ julia = "1"
 
 [extras]
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
-ImageIO = "82e4d734-157c-48bb-816b-45c225c6df19"
 ImageMagick = "6218d12a-5da1-5696-b52f-db25d2ecc6d1"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 TestImages = "5e47fb64-e119-507b-a336-dd2b206d9990"
 
 [targets]
-test = ["Test", "ImageMagick", "ImageIO", "OffsetArrays", "TestImages"]
+test = ["Test", "ImageMagick", "OffsetArrays", "TestImages"]