Remove EnableDeSSANonRootFuncArg as it is no longer used.

Change-Id: I15815f96c3708b3f80ff82ec9d29c8a10de27087

Author: jgu222

IGC/common/igc_flags.def

@@ -71,7 +71,6 @@ DECLARE_IGC_REGKEY(bool, DisableCodeHoisting,           false, "Setting this to
 DECLARE_IGC_REGKEY(bool, DisableDeSSA,                  false, "Setting this to 1/true adds a compiler switch to disable optimized De-SSA")
 DECLARE_IGC_REGKEY(bool, EnableDeSSAWA,                 true,  "[tmp]Keep some piece of code to avoid perf regression")
 DECLARE_IGC_REGKEY(DWORD, EnableDeSSAAlias,             3, "[tmp]Enable adding alias feature to DeSSA (3: dessa alias on)")
-DECLARE_IGC_REGKEY(bool, EnableDeSSANonRootFuncArg,     true, "[tmp]When this is set, formal argument is not necessarily a root value of dessa, which is true now.")
 DECLARE_IGC_REGKEY(bool, DisablePayloadCoalescing,      false, "Setting this to 1/true adds a compiler switch to disable payload coalescing optimization for all types")
 DECLARE_IGC_REGKEY(bool, DisablePayloadCoalescing_RT,   false, "Setting this to 1/true adds a compiler switch to disable payload coalescing optimization for RT only")
 DECLARE_IGC_REGKEY(bool, DisablePayloadCoalescing_Sample, false, "Setting this to 1/true adds a compiler switch to disable payload coalescing optimization for Samplers only")