Adjust rules for DE1.2 to not allow national subtypes E1-E6

Current Understanding: We need to forbid that PSPs send national forms E1-E6 in version eFormsDE 1.2. If they do everything right they should not do it, because TED and SDK-DE do not provide anything around the E1-E6 forms anymore (no efx, no structure in 1.10 anymore,…) , but PSPs could be stupid and just write eFormsDE 1.2 as a customisation ID inside an E1-E6, which would currently be accepted in DÖE because DE1.2 is generally an accepted version in DÖE, but is not the format that should be used for the national forms. PSPs have already complained that its extra effort to keep 1.1 alive only for national notices, so I see a high risk that PSPs could just use 1.2 instead. A lot of them are already switching to 1.2 at the moment, so we might get the first cases even now.

Needed Change: Remove E2-E4 from list of supported subtypes in ruleset

<let name="SUBTYPES-ALL"    value="('4', '5', '6', 'E2', '7', '8', '9', '10', '11', '12', '13', '14', '15', '16', '17', '18', '19', 'E3', '20', '21', '22', '23', '24', '25', '26', '27', '28', '29', '30', '31', '32', 'E4', '33', '34', '35', '36', '37', '38', '39', '40')" />  

Used by this rule:

<!-- Verifying that SubTypeCode is in list of expected SubTypeCodes, as seen in SUBTYPES-ALL variable  -->   
 <rule context="$SUBTYPE-CODE-NODE">      <assert id="SR-DE-3" test="($SUBTYPE = $SUBTYPES-ALL)" role="error">[SR-DE-3] SubTypeCode <value-of select="." /> is not valid. It must be a value from this list <value-of select="$SUBTYPES-ALL" />.</assert>  
  </rule>