[Cherry-pick] Simplify platformprotos

Add atom enums & messages into libstats_internal_protos and remove them
from the srcs of platformprotos

Bug: 282129591
Test: m platformprotos
Merged-In: I442822184ae02429337ff903db630028902d4d4f
Change-Id: I442822184ae02429337ff903db630028902d4d4f
(cherry picked from commit 8095ea6e0454e7192b507d10569f62425ce9fbda)
2 files changed