contrib: "set -e" behaves weird in subshells followed by OR. don't use.

This exits as expected:
```
$ cat s1.sh
#!/bin/bash
set -e
(
    echo "a"
    false
    echo "b"
)

$ ./s1.sh
a
```
This does NOT exit, seemingly because of the outer context?!
```
$ cat s2.sh
#!/bin/bash
set -e
(
    echo "a"
    false
    echo "b"
) || echo "c"

$ ./s2.sh
a
b
```

ref https://unix.stackexchange.com/questions/65532/why-does-set-e-not-work-inside-subshells-with-parenthesis-followed-by-an-or

contrib/build-linux/appimage/make_appimage.sh

@@ -181,7 +181,7 @@ info "finalizing AppDir."
     mv usr/include usr/include.tmp
     delete_blacklisted
     mv usr/include.tmp usr/include
-) || fail "Could not finalize AppDir"
+)
 
 info "Copying additional libraries"
 (