[ContextManager] Remove the put/get free context cycle

The put/get free context cycle in ContextManager::start() (if
continuation stealing is enabled) became unnecessary with
c66551bf ("[Context] Use 'jmp' instead of 'ret' to kickoff the
context").

emper/ContextManager.cpp

@@ -73,34 +73,15 @@ void ContextManager::start() {
 		return;
 	}
 
+	Context* freeContext = nullptr;
 	if constexpr (emper::CONTINUATION_STEALING) {
 		Fibril::tryResumeFibril(fibrilResumeValue);
 
-		// The code below only needs to be executed if we did a long jmp
-		// before. But optimizing for it is not worth it.  If we longjmp
-		// and can not resume the Fibril and we where not on the initial
-		// context of the Fibril, then we need to take care to recycle the
-		// context.
-		Context* currentContext = Context::getCurrentContext();
-		if (currentContext) {
-			// If we would simply call currentContext->start() here, then we
-			// would jump to an invalid address. The reason is that as soon as
-			// the Context::kickoff() is executed, the alpha function address,
-			// which was just popped of the stack, will be potentially
-			// overriden by a stack push operation. And such operations are
-			// very likely. Instead we simply free the current context here,
-			// so that it is re-initialized later on.
-
-			// TODO: Adjust the assembly to not use 'ret' to reach the
-			// kickoff function, but instead jmp. This would not destroy the
-			// kickoff's function pointer on the stack, and we could call
-			// currentContext->start() here. This would print a small
-			// performance gain.
-			putFreeContext(currentContext);
-		}
+		freeContext = Context::getCurrentContext();
 	}
 
-	Context* freeContext = getFreeContext();
+	if (!freeContext) freeContext = getFreeContext();
+
 	freeContext->start();
 }