Remove IsDependencyRoot from interface

This is equivalent to Binary() -- reduce the interface and improve
clarity.

Test: go test soong tests
Change-Id: I770f5ce79fd4d888586d31ec5e67be88153626b6

rust/binary.go

@@ -155,7 +155,3 @@ func (binary *binaryDecorator) stdLinkage(ctx *depsContext) RustLinkage {
 	}
 	return binary.baseCompiler.stdLinkage(ctx)
 }
-
-func (binary *binaryDecorator) isDependencyRoot() bool {
-	return true
-}

rust/compiler.go

@@ -289,10 +289,6 @@ func (compiler *baseCompiler) CargoOutDir() android.OptionalPath {
 	return android.OptionalPathForPath(compiler.cargoOutDir)
 }
 
-func (compiler *baseCompiler) isDependencyRoot() bool {
-	return false
-}
-
 func (compiler *baseCompiler) strippedOutputFilePath() android.OptionalPath {
 	return compiler.strippedOutputFile
 }

rust/rust.go

@@ -172,13 +172,6 @@ func (mod *Module) SanitizePropDefined() bool {
 	return mod.sanitize != nil && mod.compiler != nil
 }
 
-func (mod *Module) IsDependencyRoot() bool {
-	if mod.compiler != nil {
-		return mod.compiler.isDependencyRoot()
-	}
-	panic("IsDependencyRoot called on a non-compiler Rust module")
-}
-
 func (mod *Module) IsPrebuilt() bool {
 	if _, ok := mod.compiler.(*prebuiltLibraryDecorator); ok {
 		return true
@@ -449,7 +442,6 @@ type compiler interface {
 	SetDisabled()
 
 	stdLinkage(ctx *depsContext) RustLinkage
-	isDependencyRoot() bool
 
 	strippedOutputFilePath() android.OptionalPath
 }