Revert "Fix alignment when using PacketBuffer reserve space"

[kpschoedel]

Reverts #19244

Fixes #19289 M5 board cannot be paired due to continuous crash and rebooting

[github-actions]

PR #19293: Size comparison from c868f81 to f7ce63d

Increases (1 build for nrfconnect)

platform	target	config	section	c868f81	f7ce63d	change	% change
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	text	817260	817264	4	0.0

Full report (5 builds for mbed, nrfconnect, telink)

platform	target	config	section	c868f81	f7ce63d	change	% change
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2429848	2429848	0	0.0
			.bss	202724	202724	0	0.0
			.data	5872	5872	0	0.0
			.text	1392492	1392492	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1192179	1192179	0	0.0
			bss	141378	141378	0	0.0
			rodata	154628	154628	0	0.0
			text	817260	817264	4	0.0
	all-clusters-minimal-app	nrf52840dk_nrf52840	(read/write)	1139891	1139891	0	0.0
			bss	140595	140595	0	0.0
			rodata	131124	131124	0	0.0
			text	789312	789312	0	0.0
telink	light-switch-app	tlsr9518adk80d	(read/write)	781940	781940	0	0.0
			bss	70652	70652	0	0.0
			noinit	40416	40416	0	0.0
			text	552810	552810	0	0.0
	lighting-app	tlsr9518adk80d	(read/write)	801952	801952	0	0.0
			bss	70904	70904	0	0.0
			noinit	40416	40416	0	0.0
			text	569530	569530	0	0.0