For operands with an identical set of alternatives there is no point
in marking them commutative.  This patch removes the superfluous
constraint modifiers in vector.md and vx-builtins.md since it might
slow down reload without buying us anything.

There were even two patterns where the constraint modifier was plain
wrong: "sub<VF_HW>3" and "ior_not<VT>3". Fortunately it never had any effect.

gcc/ChangeLog:

2020-04-02  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/vector.md ("<ti*>add<mode>3", "mul<mode>3")
	("and<mode>3", "notand<mode>3", "ior<mode>3", "ior_not<mode>3")
	("xor<mode>3", "notxor<mode>3", "smin<mode>3", "smax<mode>3")
	("umin<mode>3", "umax<mode>3", "vec_widen_smult_even_<mode>")
	("vec_widen_umult_even_<mode>", "vec_widen_smult_odd_<mode>")
	("vec_widen_umult_odd_<mode>", "add<mode>3", "sub<mode>3")
	("mul<mode>3", "fma<mode>4", "fms<mode>4", "neg_fma<mode>4")
	("neg_fms<mode>4", "*smax<mode>3_vxe", "*smaxv2df3_vx")
	("*smin<mode>3_vxe", "*sminv2df3_vx"): Remove % constraint
	modifier.
	("vec_widen_umult_lo_<mode>", "vec_widen_umult_hi_<mode>")
	("vec_widen_smult_lo_<mode>", "vec_widen_smult_hi_<mode>"):
	Remove constraints from expander.
	* config/s390/vx-builtins.md ("vacc<bhfgq>_<mode>", "vacq")
	("vacccq", "vec_avg<mode>", "vec_avgu<mode>", "vec_vmal<mode>")
	("vec_vmah<mode>", "vec_vmalh<mode>", "vec_vmae<mode>")
	("vec_vmale<mode>", "vec_vmao<mode>", "vec_vmalo<mode>")
	("vec_smulh<mode>", "vec_umulh<mode>", "vec_nor<mode>3")
	("vfmin<mode>", "vfmax<mode>"): Remove % constraint modifier.