checkout: fix "branch info" memory leaks

The "checkout" command is one of the main sources of leaks in the test
suite, let's fix the common ones by not leaking from the "struct
branch_info".

Doing this is rather straightforward, albeit verbose, we need to
xstrdup() constant strings going into the struct, and free() the ones
we clobber as we go along.

This also means that we can delete previous partial leak fixes in this
area, i.e. the "path_to_free" accounting added by 96ec7b1e708 (Convert
resolve_ref+xstrdup to new resolve_refdup function, 2011-12-13).

There was some discussion about whether "we should retain the "const
char *" here and cast at free() time, or have it be a "char *". Since
this is not a public API with any sort of API boundary let's use
"char *", as is already being done for the "refname" member of the
same struct.

The tests to mark as passing were found with:

    rm .prove; GIT_SKIP_TESTS=t0027 prove -j8 --state=save t[0-9]*.sh :: --immediate
    # apply & compile this change
    prove -j8 --state=failed :: --immediate

I.e. the ones that were newly passing when the --state=failed command
was run. I left out "t3040-subprojects-basic.sh" and
"t4131-apply-fake-ancestor.sh" to to optimization-level related
differences similar to the ones noted in[1], except that these would
be something the current 'linux-leaks' job would run into.

1. https://lore.kernel.org/git/cover-v3-0.6-00000000000-20211022T175227Z-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

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