fix: remove required attr from SFTP showon fields — blocks save when not SFTP

Joomla validates required fields server-side regardless of showon
visibility. SFTP fields with required="true" block saving when
remote_storage is set to None or S3/GDrive because the hidden
fields submit empty values. Validation should be done in
ProfileTable::check() conditionally instead.

source/packages/com_mokosuitebackup/forms/profile.xml

@@ -182,7 +182,6 @@
 			label="COM_MOKOJOOMBACKUP_FIELD_SFTP_HOST"
 			description="COM_MOKOJOOMBACKUP_FIELD_SFTP_HOST_DESC"
 			maxlength="255"
-			required="true"
 			showon="remote_storage:sftp"
 		/>
 		<field
@@ -201,7 +200,6 @@
 			label="COM_MOKOJOOMBACKUP_FIELD_SFTP_USERNAME"
 			description="COM_MOKOJOOMBACKUP_FIELD_SFTP_USERNAME_DESC"
 			maxlength="255"
-			required="true"
 			showon="remote_storage:sftp"
 		/>
 		<field
@@ -222,7 +220,6 @@
 			label="COM_MOKOJOOMBACKUP_FIELD_SFTP_PASSWORD"
 			description="COM_MOKOJOOMBACKUP_FIELD_SFTP_PASSWORD_DESC"
 			maxlength="255"
-			required="true"
 			showon="remote_storage:sftp[AND]sftp_auth_type:password"
 		/>
 		<field
@@ -240,7 +237,6 @@
 			label="COM_MOKOJOOMBACKUP_FIELD_SFTP_PASSPHRASE"
 			description="COM_MOKOJOOMBACKUP_FIELD_SFTP_PASSPHRASE_DESC"
 			maxlength="255"
-			required="true"
 			showon="remote_storage:sftp[AND]sftp_auth_type:key_passphrase"
 		/>
 		<field
@@ -250,7 +246,6 @@
 			description="COM_MOKOJOOMBACKUP_FIELD_SFTP_PATH_DESC"
 			default="/backups"
 			maxlength="512"
-			required="true"
 			showon="remote_storage:sftp"
 		/>
 	</fieldset>