Revert "Support per-module MakeVars"

This reverts commit 2019658b86.

Reason for revert: broke builds where makefiles were using M4 without depending upon it

Change-Id: I18304246e7a8a8f8c2620dd2c65ed77acd256be2

android/prebuilt_build_tool.go

@@ -29,10 +29,6 @@ type prebuiltBuildToolProperties struct {
 
 	// Extra files that should trigger rules using this tool to rebuild
 	Deps []string `android:"path,arch_variant"`
-
-	// Create a make variable with the specified name that contains the path to
-	// this prebuilt built tool, relative to the root of the source tree.
-	Export_to_make_var *string
 }
 
 type prebuiltBuildTool struct {
@@ -85,12 +81,6 @@ func (t *prebuiltBuildTool) HostToolPath() OptionalPath {
 	return t.toolPath
 }
 
-func (t *prebuiltBuildTool) MakeVars(ctx MakeVarsModuleContext) {
-	if makeVar := String(t.properties.Export_to_make_var); makeVar != "" {
-		ctx.StrictRaw(makeVar, t.toolPath.String())
-	}
-}
-
 var _ HostToolProvider = &prebuiltBuildTool{}
 
 // prebuilt_build_tool is to declare prebuilts to be used during the build, particularly for use