Use new java_system_features_srcs rule in framework

Adopt the new soong rule for system feature codegen. This is an
effective no-op in terms of generated code or framework impact,
but should improve maintainability.

Test: m
Bug: 203143243
Change-Id: Ic9e399c609d98b3c4129e013b1cd50d97af632b7
1 file changed