Remove obsolete async flags in application manifest

[wridgeu]

Hey 👋

I think this can be removed

bestofui5-website/src/manifest.json

Line 44 in d358a50

"async": true,

according to sap.ui.core.IAsyncContentCreation

bestofui5-website/src/Component.ts

Lines 22 to 24 in d358a50

	// marker to identify async content creation
	// makes async: true for rootView obsolete!
	interfaces: ["sap.ui.core.IAsyncContentCreation"],

probably this one as well (based on the documentation)

bestofui5-website/src/manifest.json

Line 104 in d358a50

"async": true