arch: Remove stub cputime.h headers

arch: Remove stub cputime.h headers

Many architectures have a stub cputime.h that only include the default
cputime.h

Lets remove the useless headers, we only need to mention that we want
the default headers on the Kbuild files.

Cc: Archs <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>