stop 'encrypted database' experiment

this PR removes options to create encrypted database.
existing encrypted databases will continue working for now.

the 'encrypted database' experiment started some years ago
was never finishes and already stopped working partly,
eg. importing backups as encrypted accounts stopped working
some years ago for newer android.

in the light of Signal's "encryption key flaw",
but also recent issues with worsending core things in Delta Chat,
it seems wise to concentrate on the core things ("you have one job!"),
and not on side topics comparable few persons are interested in.

also, it will become harder to maintain that path on upcoming api changes,
leaving the database open as opening is slow is needed but will become harder,
this will make notifications tricy,
may need additional effort to run in background etc.

all that is doable,
however, it will remove resources from far more important parts,
dangerously up to a level that breaks the app - a focus is limited.

also, no one really complained as it is already partly not-working,
it was _never_ working on desktop
(where it would make much more sense),
removal on iOS was flawless, see https://github.com/deltachat/deltachat-ios/pull/2011

tl;dr: better leave the protection up to the operating system
and concentrate on other things.

jni/dc_wrapper.c

@@ -282,12 +282,6 @@ JNIEXPORT jint Java_com_b44t_messenger_DcAccounts_addAccount(JNIEnv *env, jobjec
 }
 
 
-JNIEXPORT jint Java_com_b44t_messenger_DcAccounts_addClosedAccount(JNIEnv *env, jobject obj)
-{
-    return dc_accounts_add_closed_account(get_dc_accounts(env, obj));
-}
-
-
 JNIEXPORT jint Java_com_b44t_messenger_DcAccounts_migrateAccount(JNIEnv *env, jobject obj, jstring dbfile)
 {
     CHAR_REF(dbfile);