SPR-16936 Fix PathVariable javadoc

@PathVariable's javadoc states that it supports MultiValueMap
parameters (introduced by commit df0902), but by reading through the
code, that does not seem to be the case (compare, e.g.,
PathVariableMapMethodArgumentResolver to
RequestParamMapMethodArgumentResolver).

Moreover, parsing MultipleValueMap is done according to the ";"
character, and placing such a character in a path (e.g., consider
something like "/app/{param}/show" would just break the path.

This patch fixes PathVariable's javadoc by removing the mention of
MultiValueMap.

spring-web/src/main/java/org/springframework/web/bind/annotation/PathVariable.java

@@ -29,8 +29,7 @@ import org.springframework.core.annotation.AliasFor;
  * variable. Supported for {@link RequestMapping} annotated handler methods in Servlet
  * environments.
  *
- * <p>If the method parameter is {@link java.util.Map Map&lt;String, String&gt;} or
- * {@link org.springframework.util.MultiValueMap MultiValueMap&lt;String, String&gt;}
+ * <p>If the method parameter is {@link java.util.Map Map&lt;String, String&gt;}
  * then the map is populated with all path variable names and values.
  *
  * @author Arjen Poutsma