Revert "Help: Add 3.1 release note about source file name casing"

This reverts commit ea1afd8465047bb9fc5e17525f170c21c1e0a27c.
We will try to fix this behavior instead of documenting the
regression.
Merge topic 'doc-source-case-sensitivity' into next

76e941e1 Revert "Help: Add 3.1 release note about source file name casing"