uaccess: minimize INLINE_COPY_USER-related ifdefery

uaccess: minimize INLINE_COPY_USER-related ifdefery

Now that we've got the same config selecting inline vs outline
copy_to_user() and copy_from_user(), we can simplify the corresponding
logic in the uaccess.h.

Link: https://lore.kernel.org/20260425020857.356850-4-ynorov@nvidia.com
Fixes: 1f9a8286bc0c ("uaccess: always export _copy_[from|to]_user with CONFIG_RUST")
Signed-off-by: Yury Norov <ynorov@nvidia.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>