Remove flattr from FUNDING.yml

Author: phw

.github/FUNDING.yml

@@ -9,4 +9,4 @@ github: [phw]# Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [use
 liberapay: phw # Replace with a single Liberapay username
 #issuehunt: # Replace with a single IssueHunt username
 #otechie: # Replace with a single Otechie username
-custom: ['https://flattr.com/@phw'] # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
+#custom: ['https://flattr.com/@phw'] # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']