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Fixing the linter workflow

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This should work automatically, and the previous behavior is
incorrect if we intend to use the system copy of maxima.

This new spkg-configure.m4 checks for both a "maxima" executable, and
the usability of a "maxima" package by ECL. (The latter requires a
patched maxima until a new release with commit a0d7a43e523 is made.)
Notably absent for the moment is a version check, but that should be
okay: at the moment, the only system copies of maxima that support
being used as an ECL library are those that are patched, and the only
reason to patch them is if you intend to use them with SageMath. So in
short, if a distro patches their maxima to use it with sage, we expect
it to work with sage.

This commit also moves the SAGE_MAXIMA_FAS variable handling from
ECL's spkg-configure.m4 to maxima's (where it would have belonged in
the first place, if maxima had an spkg-configure.m4 at the time.)

This patch won't be present in a system copy of maxima (at least for
now), so we disable these tests to avoid spurious failures once we
start accepting maxima from the system.

We have some old code and an old test for a memory limit that was
present in ECL 12 years ago, worked around in ticket 6772. The memory
limit is no longer in place, and would not have applied to a non-ECL
maxima from the system anyway. Since the test itself is purposely
wasteful (to ensure that we can use lots of RAM), we take this
opportunity to remove it and speed up the test suite a bit.

… directory.

This just fixes a test. The problem was noticed on Arch where, due to
some other circumstances, maxima was executed from within /usr/sbin.
But all we know for sure is that maxima will live in PATH. So we
modify the test to look only for "maxima", and not its parent
directory.

The ECL library is now contained in a separate maxima-fas package that
will pull in maxima itself.