Revert "support/testing: enable lpxelinux for syslinux runtime test"

This reverts commit 4b7f821eb5ffd017762d7db9edee460860d3cd16.

LPXELINUX is not present on 2025.02.x.

Signed-off-by: Thomas Perale <thomas.perale@mind.be>

support/testing/tests/boot/test_syslinux.py

@@ -21,7 +21,6 @@ class TestSysLinuxBase(infra.basetest.BRTest):
         """
         BR2_TARGET_SYSLINUX=y
         BR2_TARGET_SYSLINUX_ISOLINUX=y
-        BR2_TARGET_SYSLINUX_LPXELINUX=y
         BR2_TARGET_SYSLINUX_PXELINUX=y
         BR2_TARGET_SYSLINUX_MBR=y
         """