bash: nativesdk-bash does not provide /bin/bash so don't claim to

bash: nativesdk-bash does not provide /bin/bash so don't claim to

The package nativesdk-sdk-provides-dummy already provides /bin/sh and /bin/bash and
nativesdk-bash does not provide them, it provides them in ${nativesdk_bindir}. Tweak
the definition to class-target only to avoid this.

[RP: Tweaked wording to clarify]

Signed-off-by: Maanya Goenka <maanyagoenka@microsoft.com>
Signed-off-by : Alejandro Hernandez Samaniego <alhe@linux.microsoft.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>