Remove default_shared_libs

system_shared_libs has been modified to have the same behavior as
the newly added default_shared_libs, remove default_shared_libs in
favor of system_shared_libs.

This reverts Ia2349d84c70e503916f90a5d2702e135248f73df and renames
the default_shared_libs property in cc_object (which never had
system_shared_libs) to system_shared_libs.

Bug: 193559105
Test: m checkbuild
Change-Id: I46672e3a096b6ea94ff4c10e1c31e8fd010a163c

cc/cc.go

@@ -554,8 +554,7 @@ type specifiedDeps struct {
 	sharedLibs []string
 	// Note nil and [] are semantically distinct. [] prevents linking against the defaults (usually
 	// libc, libm, etc.)
-	systemSharedLibs  []string
-	defaultSharedLibs []string
+	systemSharedLibs []string
 }
 
 // installer is the interface for an installer helper object. This helper is responsible for