kernel/linux: Cleanup unneeded files from 'headers_check' and 'headers_install'

headers_install makes .install and ..install.cmd files.
headers_check makes .check and ..check.cmd files.
Remove these files uncoditionaly after installing (and checking) header files
into the sys-root.

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>
[Yann E. MORIN: reformat the patch, move hunk out of headers_check conditional]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Bare metal config options

 config KERNEL_bare_metal

     select BARE_METAL

     help

       'Bare metal' refers to those programs that run without any kernel.

       You probably want to say 'y' here if you plan to use your compiler

       to build bootloaders. It is not yet suitable to build Linux kernels,

       though, because the APCI stuff relies on the target C library headers

       being available?!?!...