Refine (optional) system_server Proguard config

Allow removal of synthetic members, as well as access modifications,
improving both inlining performance and low-risk size reduction.

Bug: 203088572,210510433
Test: SYSTEM_OPTIMIZE_JAVA=true m (validate services.jar/odex change)
Change-Id: I17fd15623351b985d49034f4de13425b31a93758