Remove download size from debuginfod progress messages if unavailable

Remove download size from debuginfod progress messages if unavailable

Currently debuginfod progress update messages include the size of
each download:

  Downloading 7.5 MB separate debug info for /lib/libxyz.so.0

This value originates from the Content-Length HTTP header of the
transfer.  However this header is not guaranteed to be present for
each download.  This can happen when debuginfod servers compress files
on-the-fly at the time of transfer.  In this case gdb wrongly prints
"-0.00 MB" as the size.

This patch removes download sizes from progress messages when they are
not available.  It also removes usage of the progress bar until
a more thorough reworking of progress updating is implemented. [1]

[1] https://sourceware.org/pipermail/gdb-patches/2022-February/185798.html