Generic/FunctionCallArgumentSpacing: update XML doc to remove info about spacing around equal sign

The FunctionCallArgumentSpacing sniff used to check for spacing around
the equal sign in the arguments of a function declaration. But this was
removed in squizlabs/PHP_CodeSniffer#2399
(commit feeda47).

This commit updates the sniff XML doc to reflect this change.

Author: rodrigoprimo

src/Standards/Generic/Docs/Functions/FunctionCallArgumentSpacingStandard.xml

@@ -1,7 +1,7 @@
 <documentation title="Function Argument Spacing">
     <standard>
     <![CDATA[
-    Function arguments should have one space after a comma, and single spaces surrounding the equals sign for default values.
+    Function arguments should have one space after a comma.
     ]]>
     </standard>
     <code_comparison>
@@ -16,22 +16,6 @@ function foo($bar,<em> </em>$baz)
         <![CDATA[
 function foo($bar,<em></em>$baz)
 {
-}
-        ]]>
-        </code>
-    </code_comparison>
-    <code_comparison>
-        <code title="Valid: Single spaces around an equals sign in function declaration.">
-        <![CDATA[
-function foo($bar, $baz<em> </em>=<em> </em>true)
-{
-}
-        ]]>
-        </code>
-        <code title="Invalid: No spaces around an equals sign in function declaration.">
-        <![CDATA[
-function foo($bar, $baz<em></em>=<em></em>true)
-{
 }
         ]]>
         </code>