Various cleanup in soong_ui to aid new feature

- Rename the "BuildX" variables to "RunX"
- Remove redundant comments
- Inline all the "what to do" based on config in build.go
- Inline some constants only used in one place

Bug: 189187214
Test: m nothing
Test: build/soong/build_test.bash
Change-Id: I111a69e642212d7938d4971283545e0d9acbb01a
Merged-In: I111a69e642212d7938d4971283545e0d9acbb01a
(cherry picked from commit d274ea9196)

cuj/cuj.go

@@ -115,7 +115,7 @@ func (t *Test) Run(logsDir string) {
 	defer f.Shutdown()
 	build.FindSources(buildCtx, config, f)
 
-	build.Build(buildCtx, config, build.BuildAll)
+	build.Build(buildCtx, config)
 
 	t.results.metrics = met
 }