Revert^2 [Pod] Remove srcs from pods default rule.

We expect too much variation in srcs across SysUI because of Recommended
Architecture, so let's just not include a default.

Bug: 307607958
Flag: EXEMPT refactor
Test: m SystemUI-core

This reverts commit 8e0b53bb.

Reason for revert: This CL wasn't root cause of compile error

Change-Id: Idc3d171442a0a50d6073909d58b40353f35a5985