main/alsa-lib: enable asserts again

The `--without-debug` flag was added silently in
e7099738. As per `./configure --help`,
this flag disable assert statements in alsa-lib. This is undesirable
since it makes library usage errors more laborious to debug or
potentially even makes them go unnoticed.

For example, see #12729 where a null pointer was passed to
snd_config_delete by alsa-utils. While the snd_config_delete function in
alsa-lib contains an assert checking that the passed config is non-null
this assert was disabled due to the aforementioned configure flag.

See also:

* https://lists.alpinelinux.org/~alpine/devel/%3C1ZU8S8ERRPKR9.35CUIBSS8QET7%408pit.net%3E
8 jobs for !22073 with alsa-lib-debug in 1 minute and 22 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Lint
passed #410092
docker-alpine x86_64
lint

00:00:24

 
  Build
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docker-alpine ci-build aarch64
build-aarch64

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passed #410099
docker-alpine ci-build armhf
build-armhf

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docker-alpine ci-build armv7
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docker-alpine ci-build ppc64le
build-ppc64le

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docker-alpine ci-build s390x
build-s390x

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docker-alpine ci-build x86
build-x86

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passed #410093
docker-alpine ci-build x86_64
build-x86_64

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