libsys: various updates

- move system calls for use by services from libminlib into libsys;
- move srv_fork(2) and srv_kill(2) from RS and into libsys;
- replace getprocnr(2) with sef_self(3);
- rename previous getnprocnr(2) to getprocnr(2);
- clean up getepinfo(2);
- change all libsys calls that used _syscall to use _taskcall, so as
  to avoid going through errno to pass errors; this is already how
  most calls work anyway, and many of the calls previously using
  _syscall were already assumed to return the actual error;
- initialize request messages to zero, for future compatibility
  (note that this does not include PCI calls, which are in need of a
  much bigger overhaul, nor kernel calls);
- clean up more of dead DS code as a side effect.

Change-Id: I8788f54c68598fcf58e23486e270c2d749780ebb

servers/ds/store.h

@@ -11,7 +11,6 @@
 
 #define NR_DS_KEYS	(2*NR_SYS_PROCS)	/* number of entries */
 #define NR_DS_SUBS	(4*NR_SYS_PROCS)	/* number of subscriptions */
-#define NR_DS_SNAPSHOT	5	/* number of snapshots */
 
 /* Base 'class' for the following 3 structs. */
 struct data_store {
@@ -26,13 +25,6 @@ struct data_store {
 			size_t length;
 			size_t reallen;
 		} mem;
-		struct dsi_map {
-			void *data;
-			size_t length;
-			void *realpointer;
-			void *snapshots[NR_DS_SNAPSHOT];
-			int sindex;
-		} map;
 	} u;
 };