* Drastically improve YamlFilesystemView file removal via batching
The `remove_file` routine has to check if the file is owned by multiple packages, so it doesn't
remove necessary files. This is done by the `get_all_specs` routine, which walks the entire
package tree. With large numbers of packages on shared file systems, this can take seconds
per file tree traversal, which adds up extremely quickly. For example, a single deactivate
of a largish python package in our software stack on GPFS took approximately 40 minutes.
This patch simply replaces `remove_file` with a batch `remove_files` routine. This routine
removes a list of files rather than a single file, requiring only one traversal per batch. In
practice this means a package can be removed in seconds time, rather than potentially hours,
essentially a ~100x speedup (ignoring initial deactivation logic, which takes about 3 minutes
in our test setup).
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