cmd/compile: remove conditional code dealing with two export formats

This removes some scaffolding introduced pre-1.7, introduced to
fix an export format bug, and to minimize conflicts with older
formats. The currently deployed and recognized format is "v1",
so don't worry about other versions. This is a step towards a
better scheme for internal export format versioning.

For #16244.

Change-Id: Ic7cf99dd2a24ad5484cc54aed44fa09332c2cf72
Reviewed-on: https://go-review.googlesource.com/27205
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/bexport.go

@@ -153,13 +153,9 @@ const debugFormat = false // default: false
 // TODO(gri) disable and remove once there is only one export format again
 const forceObjFileStability = true
 
-// Supported export format versions.
+// Current export format version.
 // TODO(gri) Make this more systematic (issue #16244).
-const (
-	exportVersion0 = "v0"
-	exportVersion1 = "v1"
-	exportVersion  = exportVersion1
-)
+const exportVersion = "v1"
 
 // exportInlined enables the export of inlined function bodies and related
 // dependencies. The compiler should work w/o any loss of functionality with
@@ -734,14 +730,7 @@ func (p *exporter) typ(t *Type) {
 			p.paramList(sig.Recvs(), inlineable)
 			p.paramList(sig.Params(), inlineable)
 			p.paramList(sig.Results(), inlineable)
-
-			// for issue #16243
-			// We make this conditional for 1.7 to avoid consistency problems
-			// with installed packages compiled with an older version.
-			// TODO(gri) Clean up after 1.7 is out (issue #16244)
-			if exportVersion == exportVersion1 {
-				p.bool(m.Nointerface)
-			}
+			p.bool(m.Nointerface) // record go:nointerface pragma value (see also #16243)
 
 			var f *Func
 			if inlineable {