example-configs: switch app-linux-usb-proxy to per-release branch

The devices API changes in R4.3 makes it complicated to use the same
code base for both R4.2 and R4.3. Use separate branches.

QubesOS/qubes-issues#9325

Author: marmarek

example-configs/qubes-os-main.yml

@@ -109,8 +109,7 @@ components:
       branch: main
   - app-linux-input-proxy:
       branch: main
-  - app-linux-usb-proxy:
-      branch: main
+  - app-linux-usb-proxy
   - app-linux-snapd-helper:
       branch: main
   - app-shutdown-idle:

example-configs/qubes-os-r4.2.yml

@@ -112,8 +112,7 @@ components:
       branch: main
   - app-linux-input-proxy:
       branch: main
-  - app-linux-usb-proxy:
-      branch: main
+  - app-linux-usb-proxy
   - app-linux-snapd-helper:
       branch: main
   - app-shutdown-idle:

example-configs/qubes-os-r4.3.yml

@@ -107,8 +107,7 @@ components:
       branch: main
   - app-linux-input-proxy:
       branch: main
-  - app-linux-usb-proxy:
-      branch: main
+  - app-linux-usb-proxy
   - app-linux-snapd-helper:
       branch: main
   - app-shutdown-idle: