apex: Deprecate legacy_android10_support prop

min_sdk_version = 29 implies that the module should support Android10.

Bug: 150431944
Test: m
Merged-In: Iad90a239898f59456900ae7816b90379b1b43406
Change-Id: Iad90a239898f59456900ae7816b90379b1b43406
(cherry picked from commit 5417f775)

Exempt-From-Owner-Approval: cp from aosp