Reproduction Steps:
1. Import attached project.
2. Select "TGA" in Assets.
3. Observe how it is imported as RGB. (Which has been fixed in case 870830)
4. Select "PSD" in Assets.
5. Observe how it is imported as RGBA.

Expected result: PSD files with no alpha should be imported as RGB.
Actual result: PSD files with no alpha are imported as RGBA.

Reproducible with: 5.5.2p3, 5.6.0f1, 2017.1.0a4
Not reproducible with: 5.4.5f1
Regression introduced in: 5.5.0p4

Note: Something related to this issue is mentioned in case 890681.