Remove leftover code from initial changelog support

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/scripts/assemble_changelog.py b/scripts/assemble_changelog.py
index b2fa96a..07e6fc5 100755
--- a/scripts/assemble_changelog.py
+++ b/scripts/assemble_changelog.py
@@ -246,10 +246,7 @@
         self.categories = OrderedDict()
         for category in STANDARD_CATEGORIES:
             self.categories[category] = ''
-        if self.header:
-            offset = (self.header + self.top_version_title).count('\n') + 1
-        else:
-            offset = 0
+        offset = (self.header + self.top_version_title).count('\n') + 1
 
         self.add_categories_from_text(input_stream.name, offset,
                                       top_version_body, True)