Merge branch 'jlebon/pr13296'

This merge gives SystemTap the ability to decode SDT operands that refer
to symbols. There are also a few code cleanups, such as:
   - Removal of SDT probing code that supports a hypothetical kernel
     mode.
   - Removal of old unused symbol table code for reading in symbols by
     reading output from nm or from a file.
   - Major refactoring of the sdt_uprobe_var_expanding_visitor::
     visit_target_symbo_arg() function to make it easier to understand
     the overall structure.
   - Strengthening of sections/note entry checks before parsing probe
     information.