Remove 3.0-specific encoding guidance (3.1.1 adjustment to 3857)

These lines were added to clarify in 3.0 what was already fixed
properly in 3.1.  Remove most of them, but keep (and reword) the
explanation of how they correlate with how the Parameter Object
fields are used.

Author: handrews

versions/3.1.1.md

@@ -1815,18 +1815,8 @@ Field Name | Type | Description
 
 See also [Appendix C: Using RFC6570 Implementations](#usingRFC6570Implementations) for additional guidance.
 
-The role of `contentType` with `application/x-www-form-urlencoded` request bodies was not described in detail in version 3.0.3 and earlier of this specification.
-To match the intent of these fields and be compatible with version 3.1 of this specification, it is RECOMMENDED that whenever any of `style`, `explode`, or `allowReserved` are present with an explicit value:
-
-* The value of `contentType`, whether it is explicitly defined or has the default value, is to be ignored
-* If any of `style`, `explode`, or `allowReserved` are _not_ present with explicit values, then they are to be treated as if they were present with their default values
-
-However, if all three of `style`, `explode`, and `allowReserved` fields are absent, it is RECOMMENDED that:
-
-* All three keywords are to be entirely ignored, rather than treated as having their default values
-* Encoding is to be based on `contentType` alone, whether it is present with an explicit value or absent and treated as having its default value
-
-This makes the presence of at least one of `style`, `explode`, or `allowReserved` with an explicit value equivalent to using `schema` with `in: query` Parameter Objects, and their absence the equivalent of using `content`, but with the media type specified in `contentType` rather than through a Media Type Object.
+Note that the presence of at least one of `style`, `explode`, or `allowReserved` with an explicit value is equivalent to using `schema` with `in: query` Parameter Objects.
+The absence of all three of those fields is the equivalent of using `content`, but with the media type specified in `contentType` rather than through a Media Type Object.
 
 ###### Encoding `multipart` Media Types