cmd/compile: remove -d=typecheckinl flag

This flag forced the compiler to eagerly type check all available
inline function bodies, which presumably was useful in the early days
of implementing inlining support. However, it shouldn't have any
significance with the unified frontend, since the same code paths are
used for constructing normal function bodies as for inlining.

Updates #57410.

Change-Id: I6842cf86bcd0fbf22ac336f2fc0b7b8fe14bccca
Reviewed-on: https://go-review.googlesource.com/c/go/+/458617
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/inline/inl.go

@@ -1096,10 +1096,6 @@ func CalleeEffects(init *ir.Nodes, callee ir.Node) {
 // the inlining tree position index, for use with src.NewInliningBase
 // when rewriting positions.
 func oldInlineCall(call *ir.CallExpr, fn *ir.Func, inlIndex int) *ir.InlinedCallExpr {
-	if base.Debug.TypecheckInl == 0 {
-		typecheck.ImportedBody(fn)
-	}
-
 	SSADumpInline(fn)
 
 	ninit := call.Init()