samples: fix bootloaders warnings

[ktaborowski]

Remove mcuboot board overlays for _ns variant,
mcuboot always use secure images.

Fix warning was assigned 'y' but got 'n':

• FPROTECT_ALLOW_COMBINED_REGIONS on nrf54l15
• MBEDTLS_CFG_FILE on nrf52840

Remove redundant PM_MCUBOOT_PAD configuration.

Remove log configuration from board overlays.

CI parameters

Github_actions:
  #(branch, hash, pull/XXX/head)
  NRF_revision: main

  # Do not change after creating PR
  Create_NRF_PR: false
Jenkins:
  test-sdk-sidewalk: nrf54l_ns

Description

JIRA ticket:

Self review

• There is no commented code.
• There are no TODO/FIXME comments without associated issue ticket.
• Commits are properly organized.
• Change has been tested.
• Tests were updated (if applicable).

[github-actions]

Sample		diff	used	total
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.hello.ble_only	RAM	0 B	91.57 KB	0 B
	ROM	16 B	316.34 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.demo	RAM	0 B	117.08 KB	0 B
	ROM	16 B	445.64 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.demo.ble_only	RAM	0 B	102.3 KB	0 B
	ROM	16 B	368 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.dut	RAM	0 B	140.83 KB	0 B
	ROM	16 B	511.21 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.dut.no_secure	RAM	0 B	140.82 KB	0 B
	ROM	16 B	503.52 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.hello	RAM	0 B	118.53 KB	0 B
	ROM	16 B	460.67 KB	0 B
nrf54l15dk/nrf54l15/cpuapp:sample.sidewalk.hello.ble_only	RAM	0 B	92.35 KB	0 B
	ROM	16 B	366.32 KB	0 B
thingy53/nrf5340/cpuapp:sample.sidewalk.demo.ble_only	RAM	0 B	106.32 KB	0 B
	ROM	16 B	351.52 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.demo	RAM	0 B	118 KB	0 B
	ROM	16 B	450.69 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.demo.ble_only	RAM	0 B	102.93 KB	0 B
	ROM	16 B	368.32 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.dut	RAM	0 B	141.65 KB	0 B
	ROM	16 B	515.75 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.dut.no_secure	RAM	0 B	141.62 KB	0 B
	ROM	16 B	507.22 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.hello	RAM	0 B	119.23 KB	0 B
	ROM	16 B	465.72 KB	0 B
nrf52840dk/nrf52840:sample.sidewalk.hello.ble_only	RAM	0 B	92.76 KB	0 B
	ROM	16 B	366.67 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.demo	RAM	0 B	111.48 KB	0 B
	ROM	16 B	395.47 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.demo.ble_only	RAM	0 B	96.56 KB	0 B
	ROM	16 B	311.97 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.dut	RAM	0 B	135.25 KB	0 B
	ROM	16 B	461.27 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.dut.no_secure	RAM	0 B	135.23 KB	0 B
	ROM	16 B	453.82 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.hello	RAM	0 B	112.98 KB	0 B
	ROM	16 B	410.77 KB	0 B
nrf5340dk/nrf5340/cpuapp:sample.sidewalk.hello.ble_only	RAM	0 B	86.64 KB	0 B
	ROM	16 B	310.55 KB	0 B
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.demo	RAM	0 B	116.3 KB	0 B
	ROM	16 B	395.66 KB	0 B
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.demo.ble_only	RAM	0 B	101.53 KB	0 B
	ROM	16 B	318.02 KB	0 B
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.dut	RAM	0 B	140.05 KB	0 B
	ROM	16 B	461.45 KB	0 B
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.dut.no_secure	RAM	0 B	140.05 KB	0 B
	ROM	16 B	458.74 KB	0 B
nrf54l15dk/nrf54l15/cpuapp/ns:sample.sidewalk.hello	RAM	0 B	117.75 KB	0 B
	ROM	16 B	410.67 KB	0 B