rt: Remove rust_task::yield. Unused

Author: brson

src/rt/rust_task.cpp

@@ -269,11 +269,6 @@ rust_task::grow(size_t n_frame_bytes)
 
 }
 
-void
-rust_task::yield() {
-    yield(0);
-}
-
 // Only run this on the rust stack
 void
 rust_task::yield(size_t time_in_us) {

src/rt/rust_task.h

@@ -164,9 +164,6 @@ rust_task : public kernel_owned<rust_task>, rust_cond
     // Print a backtrace, if the "bt" logging option is on.
     void backtrace();
 
-    // Save callee-saved registers and return to the main loop.
-    void yield();
-
     // Yields for a specified duration of time.
     void yield(size_t time_in_ms);