pw_cpu_exception_armv7m: Remove unnecessary dependency

Removes an unrelated dependency that ended up in
pw_cpu_exception_armv7m.

Change-Id: I16982949c5ff5c37625d111096d5db9708202764
diff --git a/pw_cpu_exception_armv7m/BUILD.gn b/pw_cpu_exception_armv7m/BUILD.gn
index a23a396..73b9dd2 100644
--- a/pw_cpu_exception_armv7m/BUILD.gn
+++ b/pw_cpu_exception_armv7m/BUILD.gn
@@ -28,7 +28,6 @@
     deps = [
       "$dir_pw_cpu_exception:facade",
       "$dir_pw_preprocessor",
-      "$dir_pw_sys_io:default_putget_bytes",
     ]
     public = [ "public/pw_cpu_exception_armv7m/cpu_state.h" ]
     sources = [