Remove some unused args from Blueprint.

These are: TopFile and GeneratingPrimaryBuilder.

Also re-shuffle the list of flags to make a bit more sense and finish
the rename of BuildDir and NinjaBuildDir to SoongOutDir and OutDir,
respectively.

Test: Presubmits.
Change-Id: I103ff5f09f1c0d16f695a7da5dea13b55028e33e

android/config.go

@@ -66,7 +66,7 @@ type Config struct {
 	*config
 }
 
-// BuildDir returns the build output directory for the configuration.
+// SoongOutDir returns the build output directory for the configuration.
 func (c Config) SoongOutDir() string {
 	return c.soongOutDir
 }