refactor(create_headline): remove unused country search term

- Remove countrySearchTerm from CreateHeadlineState
- Update constructors and copyWith method to reflect the removal
- Simplify the state class by removing unused properties

Author: fulleni

lib/content_management/bloc/create_headline/create_headline_state.dart

@@ -35,7 +35,6 @@ final class CreateHeadlineState extends Equatable {
     this.countriesHasMore = true,
     this.countriesIsLoadingMore = false,
     this.countriesCursor,
-    this.countrySearchTerm = '',
     this.contentStatus = ContentStatus.active,
     this.exception,
     this.createdHeadline,
@@ -55,7 +54,6 @@ final class CreateHeadlineState extends Equatable {
   final bool countriesHasMore;
   final bool countriesIsLoadingMore;
   final String? countriesCursor;
-  final String countrySearchTerm;
   final ContentStatus contentStatus;
   final HttpException? exception;
   final Headline? createdHeadline;
@@ -85,7 +83,6 @@ final class CreateHeadlineState extends Equatable {
     bool? countriesHasMore,
     bool? countriesIsLoadingMore,
     String? countriesCursor,
-    String? countrySearchTerm,
     ContentStatus? contentStatus,
     HttpException? exception,
     Headline? createdHeadline,
@@ -106,7 +103,6 @@ final class CreateHeadlineState extends Equatable {
       countriesIsLoadingMore:
           countriesIsLoadingMore ?? this.countriesIsLoadingMore,
       countriesCursor: countriesCursor ?? this.countriesCursor,
-      countrySearchTerm: countrySearchTerm ?? this.countrySearchTerm,
       contentStatus: contentStatus ?? this.contentStatus,
       exception: exception,
       createdHeadline: createdHeadline ?? this.createdHeadline,
@@ -129,7 +125,6 @@ final class CreateHeadlineState extends Equatable {
     countriesHasMore,
     countriesIsLoadingMore,
     countriesCursor,
-    countrySearchTerm,
     contentStatus,
     exception,
     createdHeadline,