R1:ce0dc9a2ba2c

Correct an apparent off-by-one error when adjusting inlines across revision changes

Summary:
See PHI1834. It's not obvious why this "+1" is present in the code, but it causes inlines to be adjusted incorrectly when a file is not modified across changes. See D21435.

Remove it, which appears to produce accurate adjustment behavior.

Test Plan:
- See D21435 for instructions to build a change, where a file with lines "A-Z" is unmodified across Diff 1 and Diff 2.
- Left inlines on lines 14, 17-19, and 16…