[API CHANGE] Deprecate css.registry.XSimpleRegistry::mergeKey

...and let its implementations just throw a RuntimeException, now that regmerge
has been removed in "[API CHANGE] Remove deprecated idlc and regmerge from the
SDK".  Deprecate css.registry.MergeConflictException along with it (though
stoc/source/implementationregistration/ still uses it internally).  And remove
the previously unused include/registry/writer.hxx along with the newly unused
include/registry/writer.h, RegistryTypeWriter, and RegistryTypeReader.

Change-Id: I10fd286617975dc0ef9f74460a3a3eab8060939d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/123615
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

udkapi/com/sun/star/registry/MergeConflictException.idl

@@ -27,6 +27,8 @@
 
 /** is thrown if entries of two registries are contradictory in the context of
     XSimpleRegistry::mergeKey()e() method.
+
+    @deprecated as XSimpleRegistry::mergeKey is deprecated as well
  */
 published exception MergeConflictException: com::sun::star::uno::Exception
 {

udkapi/com/sun/star/registry/XSimpleRegistry.idl

@@ -102,19 +102,10 @@ published interface XSimpleRegistry: com::sun::star::uno::XInterface
     boolean isReadOnly()
             raises( com::sun::star::registry::InvalidRegistryException );
 
-    /** DEPRECATED: this method lacks a registry key (better than a URL).
+    /** merges a registry under the specified key.
 
-        merges a registry under the specified key.
-
-        <p>If the key does not exist it will be created. Existing
-        keys will be overridden from keys of registry specified by
-        <var>aUrl</var>.
-
-        @throws InvalidRegistryException
-        if the registry is not open.
-
-        @throws MergeConflictException
-        if any differences occur during merging
+        @deprecated The merge functionality is deprecated and not implemented.  Implementations will
+        throw a com::sun::star::RuntimeException.
     */
     void mergeKey( [in] string aKeyName,
              [in] string aUrl )