Rename test_only_no_hashtree to generate_hashtree

In order not to introduce any changes in the system image default value
of generate_hashtree is currently set to false. Once all the APEXes that
shouldn't have hashtree enable (i.e. non-updatable ones) explicitly set
`generate_hashtree: false` default value will be switched to true.

Test: checked that are no diffs between ${OUT}/system/apex without this
  change and with this change.
Test: m
Bug: 190621617
Change-Id: I5a3144f8f6ea7dee25678af43e2b07a8c85daa9e
diff --git a/apex/builder.go b/apex/builder.go
index da8841c..d2e6ad8 100644
--- a/apex/builder.go
+++ b/apex/builder.go
@@ -629,11 +629,7 @@
 			optFlags = append(optFlags, "--assets_dir "+filepath.Dir(a.mergedNotices.HtmlGzOutput.String()))
 		}
 
-		if ctx.ModuleDir() != "system/apex/apexd/apexd_testdata" && ctx.ModuleDir() != "system/apex/shim/build" && a.testOnlyShouldSkipHashtreeGeneration() {
-			ctx.PropertyErrorf("test_only_no_hashtree", "not available")
-			return
-		}
-		if (moduleMinSdkVersion.GreaterThan(android.SdkVersion_Android10) || a.testOnlyShouldSkipHashtreeGeneration()) && !compressionEnabled {
+		if (moduleMinSdkVersion.GreaterThan(android.SdkVersion_Android10) && !a.shouldGenerateHashtree()) && !compressionEnabled {
 			// Apexes which are supposed to be installed in builtin dirs(/system, etc)
 			// don't need hashtree for activation. Therefore, by removing hashtree from
 			// apex bundle (filesystem image in it, to be specific), we can save storage.