Fix some Clang -Wunused-but-set-variable warnings

(cherry picked from commit e771804e78)

editor/project_manager.cpp

@@ -526,7 +526,6 @@ private:
 
 					Vector<String> failed_files;
 
-					int idx = 0;
 					while (ret == UNZ_OK) {
 						//get filename
 						unz_file_info info;
@@ -566,7 +565,6 @@ private:
 							}
 						}
 
-						idx++;
 						ret = unzGoToNextFile(pkg);
 					}