Revert "fix scheduling stuff to get nice round robin scheduler behavior..."

This reverts commit 30999f20b8426081e676adfc76d1c4af7b941e8e.

This commit triggers assertions and therefore cannot be used:

$ ./run.sh test/rmwprog.o
+ test/rmwprog.o
Error: assertion failed in model.cc at line 2424
stack trace:
  ./libmodel.so : ModelChecker::resolve_promises(ModelAction*)+0x3bd
  ./libmodel.so : ModelChecker::process_write(ModelAction*)+0x21
  ./libmodel.so : ModelChecker::check_current_action(ModelAction*)+0x42b
  ./libmodel.so : ModelChecker::take_step(ModelAction*)+0x39
  ./libmodel.so : ModelChecker::run()+0xa5
  ./libmodel.so : ()+0x1a3a3
  ./libmodel.so : ()+0x1e786
  ./libmodel.so : main()+0x3c
  /lib/x86_64-linux-gnu/libc.so.6 : __libc_start_main()+0xed
  test/rmwprog.o() [0x400789]
Execution 11: INFEASIBLE: [unresolved promise]
---------------------------------------------------------------------
(   0) Thread: 0    Action: uninitialized   MO: relaxed  Loc:       0x601078   Value: 0                           CV: ( 0,  0)
(   1) Thread: 1    Action: thread start    MO: seq_cst  Loc: 0x7f6cd2016898   Value: 0xdeadbeef                  CV: ( 0,  1)
(   2) Thread: 1    Action: init atomic     MO: relaxed  Loc:       0x601078   Value: 0                           CV: ( 0,  2)
(   3) Thread: 1    Action: thread create   MO: seq_cst  Loc: 0x7f6cd1410590   Value: 0x7f6cd1410560              CV: ( 0,  3)
(   4) Thread: 2    Action: thread start    MO: seq_cst  Loc: 0x7f6cd2016e08   Value: 0xdeadbeef                  CV: ( 0,  3,  4)
(   5) Thread: 2    Action: atomic rmw      MO: relaxed  Loc:       0x601078   Value: 0x1                 Rf: 9   CV: ( 0,  3,  5)
(   6) Thread: 1    Action: thread create   MO: seq_cst  Loc: 0x7f6cd14105a0   Value: 0x7f6cd1410560              CV: ( 0,  6,  0)
(   7) Thread: 3    Action: thread start    MO: seq_cst  Loc: 0x7f6cd2017338   Value: 0xdeadbeef                  CV: ( 0,  6,  0,  7)
(   8) Thread: 2    Action: atomic rmw      MO: relaxed  Loc:       0x601078   Value: 0x2                 Rf: 5   CV: ( 0,  3,  8,  0)
(   9) Thread: 3    Action: atomic rmw      MO: relaxed  Loc:       0x601078   Value: 0                   Rf: 2   CV: ( 0,  6,  0,  9)
HASH 1973598524
---------------------------------------------------------------------

Add breakpoint to line 50 in file common.cc.