flex: Remove -Werror=format-nonliteral from compiler flags

flex uses non-literal format strings in a few places.
This has been verified to be harmless in 2.6.4.

Removing -Werror=format-nonliteral here allows us to use
-Werror=format-nonliteral globally in OPTIMIZE_FOR=security mode
while keeping flex building.

Signed-off-by: Bernhard Rosenkränzer <bernhard.rosenkraenzer.ext@huawei.com>

meta-ohos-core/recipes-devtools/flex/flex_%.bbappend

+# SPDX-FileCopyrightText: Huawei Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+# flex uses non-literal format strings in a few places.
+# This has been verified to be harmless in 2.6.4.
+#
+# Removing -Werror=format-nonliteral here allows us to use
+# -Werror=format-nonliteral globally in OPTIMIZE_FOR=security mode
+# while keeping flex building.
+
+TARGET_CFLAGS_remove = "-Werror=format-nonliteral"