Remove unused BuildManager.LoadSubmissionProjectIntoConfiguration (#7924)
Remove unused BuildManager.LoadSubmissionProjectIntoConfiguration (#7924)

In #6468, the two callers of the method and the method itself were moved to `ProjectCacheService`. However, the original method remained behind as dead code.
AndyGerlicher/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild