Remove ScriptConfiguration class and move the members to LinkerScript class.

ScriptConfiguration was a class to contain parsed results of
linker scripts. LinkerScript is a class to interpret it.

That ditinction was needed because we haven't instantiated
LinkerScript early (because, IIRC, LinkerScript class was a
ELFT template function). So, when we parse linker scripts,
we couldn't directly store the result to a LinkerScript instance.

Now, that limitation is gone. We instantiate LinkerScript
at the very beginning of our main function. We can directly
store parse results to a LinkerScript instance.

llvm-svn: 315403