Clean up RAMAllocators in display related code (#9141)

esphome/components/display/display_buffer.cpp

@@ -11,7 +11,7 @@ namespace display {
 static const char *const TAG = "display";
 
 void DisplayBuffer::init_internal_(uint32_t buffer_length) {
-  ExternalRAMAllocator<uint8_t> allocator(ExternalRAMAllocator<uint8_t>::ALLOW_FAILURE);
+  RAMAllocator<uint8_t> allocator;
   this->buffer_ = allocator.allocate(buffer_length);
   if (this->buffer_ == nullptr) {
     ESP_LOGE(TAG, "Could not allocate buffer for display!");