File Vault does not delete files. What he is getting at is that, after you install OS X, and before you place any files on your SSD, you should enable File Vault's full disk encryption. This is found in System Preferences -> Security & Privacy -> File Vault. This will begin the process of encrypting your entire SSD using a password.
I am going to keep things very simple here as the underlying technology at work is complex. Basically, once the process of encrypting your entire SSD is complete all files on it and those you add to it will be stored encrypted. When you log into you Mac it will use your password as a key to 'unlock' your encrypted disk (again keeping this explanation simple) and you will see your files like always. You will be able to create new files, modify files and delete files as always.
If someone takes your disk, or turns on your laptop and they don't know your password they will not be able to access any files on the disk as they are encrypted. So for all intents and purposes to someone without the password the disk contains a bunch of random 0s and 1s that don't make up anything useful.
So using File Vault does not exactly give you secure delete functionality in the same sense as what secure delete did. However, by using it no one (without the password) will be able to access your file whether or not you delete it with regular 'non secure' delete or if you never delete it from the encrypted disk.
To me this is still somewhat less secure then explicitly secure deleting the file because secure delete would not only write random bits to the file (essentially what an encrypted file looks like when it is 'locked') but it would repeat this process multiple times. This is important with 'old fashioned' hard drives (non-SSD) because when you write a file to them, even if you overwrite the file with random bits, there is still a physical residual magnetic signature which can be used to recover them. The more times you write random bits over it the harder and harder it becomes to read the original signature. Think of it like you dripped some spaghetti sauce on your white shirt. You spray it with oxyclean and wash it. The first time you take it out of the wash you can still make out some of the stain. That's the residual signature that can be used to recover your deleted file. So you spray it again and repeat the wash. The next time there's even less of a stain. You rinse and repeat until you can't see it anymore.
However, the problem with that approach with SSD (flash) drives is that flash memory/drives physically store data differently than a traditional magnetic hard drive does. In addition sophisticated controller software is used to manage how and where data is written to and deleted from them to ensure performance and longevity. Again all needed due to the underlying physical characteristics of flash based storage. In short, unless you use tools from the flash drives' manufacturer for secure deletion, there is no way for an operating system to directly guarantee secure deletion. Again, I am keeping things very simple here. If you want to learn more Google is your friend (secure delete SSD).
So I can understand the general principal of removing the option, however, many people still use non SSD drives like external USB, SCSI, Firewire etc. and may want to securely delete a file from it. From that standpoint this is a loss of convenient functionality. For those folks your best bet is either a 3rd party utility if you want a GUI, or use the 'srm' command from the terminal. Neither option is quite as convenient as the original functionality was.
