Skip dexbootjar check using AllowMissingDependencies flag

Soong checks that every module part of a bootclass_fragment provides a
dex boot jar file, even if the module is not a dependency of vendor.img

Using AllowMissingDepdencies() to skip this check allows vendors to be
more aggressive in removing projects from their source tree

Test: In build/soong, run go test ./...
Test: m nothing
Bug: 196306898
Bug: 192616764
Change-Id: I78b062afdc19a6a3251aa8552230f3fcf334b6fb

apex/apex_test.go

@@ -5090,6 +5090,12 @@ func TestBootDexJarsFromSourcesAndPrebuilts(t *testing.T) {
 		// find the dex boot jar in it. We either need to disable the source libfoo
 		// or make the prebuilt libfoo preferred.
 		testDexpreoptWithApexes(t, bp, "module libfoo does not provide a dex boot jar", preparer, fragment)
+		// dexbootjar check is skipped if AllowMissingDependencies is true
+		preparerAllowMissingDeps := android.GroupFixturePreparers(
+			preparer,
+			android.PrepareForTestWithAllowMissingDependencies,
+		)
+		testDexpreoptWithApexes(t, bp, "", preparerAllowMissingDeps, fragment)
 	})
 
 	t.Run("prebuilt library preferred with source", func(t *testing.T) {