dts: remove cris & metag dts hard link file

arch cris & metag have been removed from supported archs.
The dts hard link files should also be removed, or the ctags
tool will give warning.

execute"ctags -R", output:
ctags: Warning: cannot open source file
"scripts/dtc/include-prefixes/cris" : No such file or directory
ctags: Warning: cannot open source file
"scripts/dtc/include-prefixes/metag" : No such file or directory

Signed-off-by: Liu Changcheng <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>