How to reproduce:
1. Create a new Unity project
2. Drag and drop the attached "File.asmdef" file into the Assets folder (in the Project window)
3. Click on the file
4. Observe the Console window

Expected result: No errors; the occurrence of Linux 32-bit is automatically removed from the 'includePlatforms' of an .asmdef file.
Actual result: "Platform name 'LinuxStandalone32' not supported." and "ArgumentException: Unknown platform 'LinuxStandalone32'" console errors are thrown; thus, Play mode cannot be entered.

Reproducible with - 2019.2.0a3, 2019.2.0a6
Not reproducible with - 2017.4.21f1, 2018.3.7f1, 2019.1.0b5, 2019.2.0a2

Note: "ArgumentException: Unknown platform 'LinuxStandalone32'" occurs only on 2019.2.0a6 (when clicking on "File.asmdef" file)

Fixed in 2019.2.0a13