Misc simplifications

[TerrorJack]

Before we drop our custom object format and linking logic, we need to do some housekeeping.

• Simplify default entry script. The previous one is wrong and doesn't handle the error properly anyway.
• Work with a unified symbol table instead of function/data offset tables.
• Drop wasm globals logic.
• Drop SPT logic.
• Drop HaskellIR logic, only process Cmm.
• Drop uninitialized segments logic, CmmUninitialized is always a 0-initialized buffer now.
• Drop staticsType logic.
• Drop usedCCalls.
• Don't use RTS internal arena. The less hacks the better given recent segfaults.
• Drop redundant wasi-sdk reference, ensure we use the same checkout from ghc-asterius