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>

 # Default test suite configuration

 # Default DejaGnu configuration

 DG_TOOLNAME = gcc

 DG_TARGET_HOSTNAME = 127.0.0.1

 DG_TARGET_USERNAME = root

 # Default tests

 DG_C_TESTS = 

 DG_CPP_TESTS =