Flat theme: un-deprecate (#5316)

* Update metadata.json

* Update 05_Configuration.md

docs/en/users/05_Configuration.md

@@ -22,7 +22,7 @@ There’s no accounting for tastes, which is why FreshRSS offers 13 official the
 | Blue Lagoon     |Mister aiR | No longer supported. Will be removed with FreshRSS V1.22.0 |
 | Dark | AD | |
 | Dark pink | Miicat_47 | |
-| Flat design | Marien Fressinaud | No longer supported. Will be removed with FreshRSS V1.22.0 |
+| Flat design | Marien Fressinaud | |
 | Mapco | Thomas Guesnon  | |
 | Nord theme | joelchrono12 | |
 | Origine | Marien Fressinaud | (default theme) |

p/themes/Flat/metadata.json

@@ -4,6 +4,5 @@
   "description": "Thème plat pour FreshRSS",
   "version": 0.2,
   "files": ["_frss.css", "flat.css"],
-  "deprecated": true,
 	"theme-color": "#34495e"
 }