syscalls: Remove file path comments from headers

Source file locations for syscall definitions can change over a period
of time. File paths in comments get stale and are hard to maintain long
term. Also, their usefulness is questionable since it would be easier to
locate a syscall definition using the SYSCALL_DEFINEx() macro.

Remove all source file path comments from the syscall headers. Also,
equalize the uneven line spacing (some of which is introduced due to the
deletions).

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>