While editing posts I mostly delete Thanks! and Sorry for my inglese and those edits are accepted. I don't have a problem writing Edit Summary as I edited grammar and spelling also. What if I only deleted this lines, what should I write to Edit Summary?
For this kind of thing, I usually write removed unnecessary text. It's clear enough that new users can understand why it was removed, and works for "Hello", "Thanks", and "Sorry" type messages.
And as others have pointed out, I really try to find something more to fix than just that -- grammar, typos, formatting, etc.
I would suggest not performing those edits at all, until you have enough reputation to edit without the suggested edit queue. If the only change you make is removing those statements, you are risking having your edits rejected as Too Minor. Some people will accept them, but many (including myself) won't. The reason is that suggested edits require the work of four people (one editor + 3 reviewers; 2 reviewers on most sites), so if they don't make a significant improvement, it is a waste of time and energy. Once you don't need the queue anymore, you can make these edits freely, since it only takes you.
To actually answer the question, I would suggest something like "removed thanks" or "removed noise". Once you have enough reputation to edit without the queue, you can also not leave a message at all, and the system will fill in the default "deleted XXXX characters in body".
See this post for a discussion of whether these edits should be accepted or not.
I would post it as "Removed greeting." When I started up, I always did a greeting, and they always go removed with the subject "Removed greeting."
ughoavgfhw said, if you don't have the reputation to edit without peer review, don't do it. You add stress to the reviewers, and it wastes everybody's time because someone was trying to be nice when people are really trying to clean up the site.
I don't really mind the greeting either way; it is just there or not, it doesn't affect the content and I usually skim the question and skip it.
And because I couldn't resist the irony: Thanks for viewing!
I just say "de-thanked", and so far nobody has asked for a link to the meta/FAQ as to why. It's probably too terse, but so far it has been sufficient.
I have yet to have one reverted, but that could just be luck.
I agree with the sentiment that if it's the only thing you're editing, don't do it unless you no longer fall into the review queue, otherwise it will almost skyways be rejected as "too trivial", and rightfully so.