What is the difference between Image Inpainting and Image Denoising?
Inpainting solves a binary problem of missing data. These masked or missing pixels to not contain information that is used in the reconstruction. Also, is it assumed that non missing pixels are to remain as is. 

Denoising usually refers to the situation where all the pixels contain some noise component, which often also has some global prior independent of the image content. The algorithm tries to remove the noise from all the pixels, and uses the information inside these noisy pixels for the reconstruction and estimation. 

The problems are not unrelated and could be reduced to private extreme cases of each other but in general they solve different types of problems.