Remove deprecated CSP child-src
Remove deprecated CSP child-src

It's been probably long enough since
https://github.com/FreshRSS/FreshRSS/pull/1099

FreshRSS/FreshRSS,Alkarex/FreshRSS,aledeg/FreshRSS,romibi/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,romibi/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,aledeg/FreshRSS,Alkarex/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,FreshRSS/FreshRSS