Checks if the parameters are all simple strings (have a content type of "text/plain").
Create a new #GHashTable which contains the name and value of all string (content type of text/plain) parameters.
The values are owned by the #RestParams, so don't destroy the #RestParams before the hash table.
Remove the #RestParam called name
.
a parameter name
Decrements the reference count of self
by one, freeing the structure when
the reference count reaches zero.
Create a new #RestParams.