fix: rm unique constraint on profile photo link

DESCRIPTION
    If user hasn't configured a profile photo on their forge instance,
    it would point to the default photo of the forge instance, which
    might be the same for all users without a profile photo on that
    forge instance.

db/db-core/src/errors.rs

@@ -44,10 +44,6 @@ pub enum DBError {
     #[error("User HTML link is already taken")]
     DuplicateUserLink,
 
-    /// User profile photo link Type is already taken
-    #[error("User profile photo link is already taken")]
-    DuplicateProfilePhotoLink,
-
     /// Topic is already taken
     #[error("Topic is already taken")]
     DuplicateTopic,

db/db-sqlx-sqlite/migrations/20220405113942_world_forges.sql

@@ -24,7 +24,7 @@ CREATE TABLE IF NOT EXISTS starchart_users (
 	hostname_id INTEGER NOT NULL REFERENCES starchart_forges(ID) ON DELETE CASCADE,
 	username TEXT NOT NULL,
 	html_url TEXT NOT NULL UNIQUE,
-	profile_photo_html_url TEXT DEFAULT NULL UNIQUE,
+	profile_photo_html_url TEXT DEFAULT NULL,
 	added_on INTEGER NOT NULL,
 	last_crawl_on INTEGER NOT NULL,
 	ID INTEGER PRIMARY KEY NOT NULL

db/db-sqlx-sqlite/src/errors.rs

@@ -40,8 +40,6 @@ pub fn map_register_err(e: Error) -> DBError {
                 DBError::DuplicateForgeType
             } else if msg.contains("starchart_users.html_url") {
                 DBError::DuplicateUserLink
-            } else if msg.contains("starchart_users.profile_photo_html_url") {
-                DBError::DuplicateProfilePhotoLink
             } else if msg.contains("starchart_project_topics.name") {
                 DBError::DuplicateTopic
             } else if msg.contains("starchart_repositories.name") {