Clean up OWNERS regarding legacy dexopt.

The cleanup on frameworks/base has been done. Updating the OWNERS files
to only keep our ownership on a minimal set of files that we still own.

Bug: 258223472
Bug: 6527146
Test: Presubmit
Flag: EXEMPT DOCS_ONLY
Change-Id: Ib92c1843fb02824c872502db460eb29fd3e50e61