docs: remove incorrect 400 response from DELETE endpoint (#248)

- Remove invalid Bad Request response code from DELETE OpenAPI spec
- Refactor squad number lookup test to use stream filter vs hardcoded index

Author: nanotaboada

src/main/java/ar/com/nanotaboada/java/samples/spring/boot/controllers/PlayersController.java

@@ -245,7 +245,6 @@ public ResponseEntity<Void> put(@PathVariable Long id, @RequestBody @Valid Playe
     @Operation(summary = "Deletes a player by ID")
     @ApiResponses(value = {
             @ApiResponse(responseCode = "204", description = "No Content", content = @Content),
-            @ApiResponse(responseCode = "400", description = "Bad Request", content = @Content),
             @ApiResponse(responseCode = "404", description = "Not Found", content = @Content)
     })
     public ResponseEntity<Void> delete(@PathVariable Long id) {

src/test/java/ar/com/nanotaboada/java/samples/spring/boot/test/controllers/PlayersControllerTests.java

@@ -318,7 +318,10 @@ void searchByLeague_noMatches_returnsOkWithEmptyList()
     void searchBySquadNumber_playerExists_returnsOkWithPlayer()
             throws Exception {
         // Arrange
-        PlayerDTO playerDTO = PlayerDTOFakes.createAll().get(9); // Messi is at index 9
+        PlayerDTO playerDTO = PlayerDTOFakes.createAll().stream()
+                .filter(player -> player.getSquadNumber() == 10)
+                .findFirst()
+                .orElseThrow();
         Mockito
                 .when(playersServiceMock.searchBySquadNumber(10))
                 .thenReturn(playerDTO);