Delete unused code

Add static to internal functions

Profiling: Improve !defined(PETSC_USE_LOG) #defines

- If we cast macro arguments to void, we can avoid unused errors that have
forced lots of conditionally included code like this:

```c
#if def

Profiling: Improve !defined(PETSC_USE_LOG) #defines

- If we cast macro arguments to void, we can avoid unused errors that have
forced lots of conditionally included code like this:

```c
#if defined(PETSC_USE_LOG)
PetscLogEvent event;
#endif
```

- Having global counters like petsc_TotalFlops externed event
if !PetscDefined(USE_LOG) helps to remove a lot of needless
`#ifdef`s around code that can instead be placed in
`if (PetscDefined(USE_LOG)) {}` blocks.

show more ...

Lint apply: mat

docs: additional chapter_ -> ch_ change in main after merge of release changes from !6520

Don't use PetscMemcpy() or PetscArraycpy() to copy the ops struct

Fix MatConvert for SELLCUDA

MatConvert functions for SELLCUDA did not work properly. MatConvert_Basic was picked.