Config: Remove legacy configuration

[mkannwischer]

mldsa-native still carries the the legacy configuration options:

mldsa-native/mldsa/mldsa_native.h

Lines 34 to 50 in 13977d0

	* # Legacy configuration (deprecated)
	*
	* Instead of providing the config file used for the build, you can
	* alternatively set the following configuration options prior to
	* including this header.
	*
	* This method of configuration is deprecated.
	* It will be removed in mldsa-native-v2.
	*
	* - MLD_CONFIG_API_PARAMETER_SET [required]
	*
	* The parameter set used for the build; 44, 65, or 87.
	*
	* - MLD_CONFIG_API_NAMESPACE_PREFIX [required]
	*
	* The namespace prefix used for the build.
	*

As far as I know, none of our consumers is still using that configuration. I suggest removing the configuration prior to a non-beta release. mlkem-native will also remove that config in v2.