tests,base: Delete the SymbolTable::load method and symtest test.

tests,base: Delete the SymbolTable::load method and symtest test.

This test expects to load a symbol file using the load method of gem5's
SymbolTable class, and then to search through it for a given symbol or
address.

Unfortunately, the type of file it expects to load has a format where
each line is of the form:

0x00000000, symbol_name

where the numerical part is the address of the symbol, and the part
after the comma is the symbol name. I have not been able to find any
tool which outputs a symbol file in this format, or any tool for
inspecting an existing object file which will output symbols in this
format. I looked at objdump, objcopy, nm, and the map file format output
by gnu's linker. nm has 3 different output formats, none of which match.
Usually when working with ELF files, one would just generate a new ELF
file which only had debugging information like the symbol table, and
then strip the symbols out of the original.

Since this file format seems to have been invented from thin air, there
isn't really a good way to generate a canonical file to test the loading
code against, nor is being able to load this obscure format likely to be
useful to anybody. If someone *did* want to load an external symbol
table, they would use the ELF loader and not this.

This CL deletes both this test, and the loading code in SymbolTable.

Change-Id: I20402e3f35e54d1e186a92d9c83d1c06ec86bf7d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40620
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>