Revert "Temporary debg output to find out why tinderboxes still don't find program"

This reverts commit d36dc7b3.  Turns out e.g.
tb75-lilith has a 'file' command that doesn't print "execfn:" information, just

> /home/tdf/lode/jenkins/workspace/lo_tb_master_linux_dbg/workdir/UITest/calc_demo/done.core/core.24697: ELF 64-bit LSB core file x86-64, version 1 (SYSV), SVR4-style, from '/home/tdf/lode/jenkins/workspace/lo_tb_master_linux_dbg/instdir/program/soffice'

(<https://ci.libreoffice.org/job/lo_tb_master_linux_dbg/13930/console>), but
with a truncated "from:" path, so would probably be little benefit to try to get
the path from the "from:" instead of (or in addition to) the "execfn:"
information (where the latter appears to be more accurate at least with my local
file-5.29-4.fc25.x86_64).

solenv/bin/gdb-core-bt.sh

@@ -25,7 +25,6 @@ then
             GDBCOMMANDFILE=$(mktemp)
             printf "info registers\nthread apply all backtrace full\n" \
                 >"$GDBCOMMANDFILE"
-file "$COREFILE"
             guess=$(file "$COREFILE")
             guess=${guess#* execfn: \'}
             guess=${guess%%\'*}