USB: Remove USB-related sources.

The Android emulator doesn't support USB, removing these files
reduces the upstream integration work.

Change-Id: Id6b40808092e118e11924c30ca77bd366f95d12c
diff --git a/Makefile.common b/Makefile.common
index 09da93f..7101acb 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -485,12 +485,9 @@
 endif
 
 ifeq ($(HOST_OS),linux)
-    CORE_MISC_SOURCES += hw/usb/usb-linux.c \
-                         util/compatfd.c \
+    CORE_MISC_SOURCES += util/compatfd.c \
                          util/qemu-thread-posix.c \
                          android/camera/camera-capture-linux.c
-else
-    CORE_MISC_SOURCES += hw/usb/usb-dummy-android.c
 endif
 
 ifeq ($(HOST_OS),windows)