cmd/compile: remove go119UseJumpTables flag

Change-Id: Iaaac46e96b74289096ce0c6186c73000d1fc6faa
Reviewed-on: https://go-review.googlesource.com/c/go/+/463224
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: randall77

src/cmd/compile/internal/walk/switch.go

@@ -286,11 +286,10 @@ func (s *exprSwitch) search(cc []exprClause, out *ir.Nodes) {
 
 // Try to implement the clauses with a jump table. Returns true if successful.
 func (s *exprSwitch) tryJumpTable(cc []exprClause, out *ir.Nodes) bool {
-	const go119UseJumpTables = true
 	const minCases = 8   // have at least minCases cases in the switch
 	const minDensity = 4 // use at least 1 out of every minDensity entries
 
-	if !go119UseJumpTables || base.Flag.N != 0 || !ssagen.Arch.LinkArch.CanJumpTable || base.Ctxt.Retpoline {
+	if base.Flag.N != 0 || !ssagen.Arch.LinkArch.CanJumpTable || base.Ctxt.Retpoline {
 		return false
 	}
 	if len(cc) < minCases {