Fix non valid SafeString flag codes (#1135)

## Description:
Removed unicode in the following flag file names to prevent error, which
lead to not be able to start a game with it.

- Ceará
- 1_Northern Uí Néill
- Pará
- São Paulo
- 1_Southern Uí Néill

related to https://github.com/openfrontio/OpenFrontIO/pull/1133

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

ghisloufou

resources/maps/Britannia.json

@@ -115,7 +115,7 @@
       "coordinates": [564, 845],
       "name": "Southern Uí Néill",
       "strength": 3,
-      "flag": "1_Southern Uí Néill"
+      "flag": "1_Southern Ui Neill"
     },
     {
       "coordinates": [639, 680],
@@ -133,7 +133,7 @@
       "coordinates": [416, 678],
       "name": "Northern Uí Néill",
       "strength": 3,
-      "flag": "1_Northern Uí Néill"
+      "flag": "1_Northern Ui Neill"
     },
     {
       "coordinates": [1869, 1308],

src/client/data/countries.json

@@ -404,7 +404,7 @@
     "name": "Cayman Islands"
   },
   {
-    "code": "Ceará",
+    "code": "Ceara",
     "continent": "South America",
     "name": "Ceará"
   },
@@ -1501,7 +1501,7 @@
     "name": "Northern Mariana Islands"
   },
   {
-    "code": "1_Northern Uí Néill",
+    "code": "1_Northern Ui Neill",
     "continent": "Europe",
     "name": "Northern Uí Néill"
   },
@@ -1566,7 +1566,7 @@
     "name": "Papua New Guinea"
   },
   {
-    "code": "Pará",
+    "code": "Para",
     "continent": "South America",
     "name": "Pará"
   },
@@ -1803,7 +1803,7 @@
     "name": "Sao Tome and Principe"
   },
   {
-    "code": "São Paulo",
+    "code": "Sao Paulo",
     "continent": "South America",
     "name": "São Paulo"
   },
@@ -1941,7 +1941,7 @@
     "name": "South Sudan"
   },
   {
-    "code": "1_Southern Uí Néill",
+    "code": "1_Southern Ui Neill",
     "continent": "Europe",
     "name": "Southern Uí Néill"
   },