This was not conceptually an enum, but rather a collection of unrelated
constants:
- two constants for use as placeholder for symbol IDs at different places
- one constant for the default number of arguments

Performed using modernize-use-equals-default from clang-tidy.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-equals-default.html

This reverts commit 28ffa9c56fd021cc75415aeafc13d3810d1b3132, reversing
changes made to 60b3577a09f3eb9cf3cc590241343b1f0fee8706.

Conflicts:
	preprocessor/Shocks.cc
	preprocessor/SymbolTable.cc