Remove installed header rule on $(..)include/%.h

Remove installed header rule on $(..)include/%.h

On x86-64 machine with

[hjl@gnu-cfl-3 x86-glibc]$ ls -l /usr/include/asm/prctl.h sysdeps/unix/sysv/linux/x86_64/include/asm/prctl.h
-rw-r--r-- 1 hjl  hjl   825 Jan  9 09:41 sysdeps/unix/sysv/linux/x86_64/include/asm/prctl.h
-rw-r--r-- 1 root root 1170 Nov 27 16:00 /usr/include/asm/prctl.h
[hjl@gnu-cfl-3 x86-glibc]$

glibc configured with --enable-cet build failed:

make[2]: Entering directory '/export/gnu/import/git/gitlab/x86-glibc/iconv'
../Makerules:327: update target
'/export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/gnu/lib-names-64.h'
due to: /export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/gnu/lib-names-64.stmp
:
../Makeconfig:1216: update target
'/export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/libc-modules.h'
due to: /export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/libc-modules.stmp
:
../Makerules:1126: update target '/usr/include/asm/prctl.h' due to:
../sysdeps/unix/sysv/linux/x86_64/64/../include/asm/prctl.h
force-install
/usr/bin/install -c -m 644
../sysdeps/unix/sysv/linux/x86_64/64/../include/asm/prctl.h
/usr/include/asm/prctl.h
/usr/bin/install: cannot remove '/usr/include/asm/prctl.h': Permission denied
make[2]: *** [../Makerules:1126: /usr/include/asm/prctl.h] Error 1
make[2]: Leaving directory '/export/gnu/import/git/gitlab/x86-glibc/iconv'
make[1]: *** [Makefile:484: iconv/subdir_lib] Error 2
make[1]: Leaving directory '/export/gnu/import/git/gitlab/x86-glibc'
make: *** [Makefile:9: all] Error 2

This is triggered by the rule in Makerules:

$(inst_includedir)/%.h: $(..)include/%.h $(+force)
  $(do-install)

Since no files under include/ should be installed, remove it from
Makerules.

Tested it on x86-64.  There are no differences in the installed header
files.