fix: remove debug value print calls from jpeg_decoder

[ZaLiTHkA]

while using version 2.1.0 to process a bunch of JPG image files, I kept seeing output in my terminal with Orientation: 1, but I could not figure out where it was coming from...

digging a little deeper, I discovered two print() commands causing this in the jpeg_decoder.dart library file, specifically here and here.

after "fixing" the line 81 (by removing print() call), I noticed that the orientation variable definition on line 64 was reporting as "unused"... but simply removing the final keyword from the re-assignment of this variable on line 88 cleared that up.

I've forked and modified this project locally for my own usage, I'll

[CaiJingLong]

Thank for PR.