Remove obsoleted bash script

[squell]

It was only used for generating / combining coverage data from the test framework. But that cannot be done "in production mode"; please see the compliance-coverage branch for an updated and improved version of this script (and the associated changes necessary to use it meaningfully).

[squell]

By the "boy scout rule", this also makes this change (and similar ones in the unit tests):

 /// Check whether a path points to a regular file and any executable flag is set
-pub(crate) fn is_valid_executable(path: &PathBuf) -> bool {
+pub(crate) fn is_valid_executable(path: &Path) -> bool {
     if path.is_file() {

Since having a &PathBuf as an argument to a function is a bit strange; and the only reason it was done was to avoid having to write a closure.

[squell]

I didn't release the crucial role this bash script was playing in our automated tests. All the more reason to remove it.