Tracking issues for removing the `newlib` feature

[mkroening]

We should get C application support on par with the Rust application support and remove most special cases for C.

• feat: remove spinlock syscalls #656
• feat(newlib): remove lwIP support #1165
• feat(newlib): remove recmutex system calls #1166
• fix(x86_64/newlib): remove unused import #1169
• Remove semaphore