Remove checking vCont;s in exec_cmd_expect_vCont_count

Remove checking vCont;s in exec_cmd_expect_vCont_count

Nowadays, in the range-stepping tests, we check not only the number of
vCont;r packets but also the number of vCont;s packets, because we think
the remote target which can do range stepping must support single step.

However, if we turn displaced stepping on, the remote target (GDBserver)
can do range stepping, and support single step, but GDB may decide to
resume instructions in the scratchpad rather than single step them one
by one for displaced stepping.  For example, when aarch64 GDB debugs
arm linux program with aarch64 GDBserver, GDBserver supports both range
stepping and single step, but GDB (with the gdbarch for arm-linux)
decides resume instructions in the scratchpad, so in the RSP traffic,
there is no vCont;s packet at all, and some range-stepping.exp tests
fail,

FAIL: gdb.base/range-stepping.exp: multi insns: next: vCont;s=1 vCont;r=1

This patch is to get rid of the checking to the number of vCont;s in
exec_cmd_expect_vCont_count.

gdb/testsuite:

2015-10-21  Yao Qi  <yao.qi@linaro.org>

	* lib/range-stepping-support.exp (exec_cmd_expect_vCont_count):
	Remove argument exp_vCont_s.
	* gdb.base/range-stepping.exp: Callers updated.
	* gdb.trace/range-stepping.exp: Likewise.