gn2bp: Remove empty srcs cc_object from blueprint

* This was failing the pre-submits are cc_objects are compilable modules but they failed to compile due to empty srcs. However, this didn't affect the compilation of Cronet as the empty cc_objects are never in the path of compilation of Cronet because their attributes are propagated up the tree.

Test: m
Change-Id: I7cc87d53d4f460ef4958d5ecfb23ac28662fdbdc
3 files changed