[libc][NFC] Fix delete operator linkage names after switch to LIBC_NAMESPACE. (#67475)

The name __llvm_libc was mass-replaced with LIBC_NAMESPACE which ended
up changing the "__llvm_libc" prefix of the delete operator linkage names to
"LIBC_NAMESPACE". This change corrects it by changing the namespace prefix
to "__llvm_libc_<version info>".