Remove obsolete commandName attribute in spring-form.tld

Since support for the commandName attribute was removed from the
implementation of FormTag in Spring Framework 5.0, the presence of the
commandName attribute in the spring-form.tld file is no longer valid
and can lead one to assume that the commandName attribute is still
supported -- for example when using code completion in a JSP editor.

This commit therefore removes the obsolete commandName attribute in
spring-form.tld.

Closes gh-26337

spring-webmvc/src/main/resources/META-INF/spring-form.tld

@@ -130,12 +130,6 @@
 			<required>false</required>
 			<rtexprvalue>true</rtexprvalue>
 		</attribute>
-		<attribute>
-			<description>DEPRECATED: Use "modelAttribute" instead.</description>
-			<name>commandName</name>
-			<required>false</required>
-			<rtexprvalue>true</rtexprvalue>
-		</attribute>
 		<attribute>
 			<description>HTML Required Attribute</description>
 			<name>action</name>