Remove dead code and unexport some calls

"make check-api-unused" informs us about code that is not used anymore
or that is exported but only used internally. Fix these all over the
place.

src/core/execute.c

@@ -155,7 +155,7 @@ _pure_ static const char *tty_path(const ExecContext *context) {
         return "/dev/console";
 }
 
-void exec_context_tty_reset(const ExecContext *context) {
+static void exec_context_tty_reset(const ExecContext *context) {
         assert(context);
 
         if (context->tty_vhangup)