arch: remove stale comments "UAPI Header export list"

These comments are leftovers of commit fcc8487d

 ("uapi: export all
headers under uapi directories").

Prior to that commit, exported headers must be explicitly added to
header-y. Now, all headers under the uapi/ directories are exported.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/alpha/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/arc/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/arm/include/uapi/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd-common.h

arch/arm64/include/uapi/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += errno.h

arch/c6x/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/h8300/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/hexagon/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/ia64/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_64.h

arch/m68k/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/microblaze/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/mips/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_n32.h

arch/nds32/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += bpf_perf_event.h

arch/nios2/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/openrisc/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += auxvec.h

arch/parisc/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/powerpc/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/riscv/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generic-y += setup.h

arch/s390/include/uapi/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/sh/include/uapi/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h

arch/sparc/include/uapi/asm/Kbuild

-# UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
 generated-y += unistd_32.h