scripts/snap_build.sh: remove --destructive-mode

As far as I have gathered this morning, snapcraft has 3 modes of
operation: 1) Host, 2) Multi-pass, 3) LXD.

According to `snapcraft build --help` the --destructive-mode flag
implies using the 1) Host above.

Since we've had mild issues [1] when upgrading our snap package
generation from Ubuntu 20.04 to 22.04, and since apparently LXD
is the default mode for snapcraft when using 22.04 (or core22,
not sure), I'm testing removing this flag to see what happens.

But I think this will:
- Either break the build, or
- Not help with any of the issues above, or
- Not change anything, because maybe we're pinning a snapcraft
version (a channel actually) that is still too old (in the sense
that LXD is still not the default in this case).

[1] https://forum.snapcraft.io/t/gtk-related-issues-when-upgrading-snap-pkg-generation-from-20-04-to-22-04/36537

scripts/snap_build.sh

@@ -12,4 +12,4 @@ rm -rf ./staging
 make
 make install
 
-snapcraft --destructive-mode
+snapcraft