vndk-def: Update README.md

This commit removes some stale descriptions in README.md.

Test: Run vndk_definition_tool.py as described.
Change-Id: Ib5dc7f2983d728105cfc2a41eeb4d5d4ae3fa965
(cherry picked from commit 63faec7330f2b5cebf3df710e255ae7a2a36423d)
1 file changed