Edits for the HTTP compression post

[dmuelle]

per slack comment from @covener :

https://openliberty.io/blog/2020/04/22/http-response-compression.html
We should remove serverPreferredAlgorithm="deflate|gzip|x-gzip|zlib|identity|none" from the codeblocks. They are incorrect (you have to pick one of those values, not all of them and the separator) and not operative parts of the example.
In the first example, the list of types should also be dropped leaving just

[dmuelle]

changes merged to pro in #4099