Remove critical section hooks to enhance MISRA conformance

[pavel-kirienko]

Remove critical section enter/leave hooks:

o1heap/o1heap/o1heap.h

Lines 98 to 99 in bd93277

	const O1HeapHook critical_section_enter,
	const O1HeapHook critical_section_leave);

Equivalent behaviors can be implemented by wrapping library calls in custom user code instead.

[jrahlf]

The README should be changed accordingly, currently it says

In the case of concurrent environments, also pass pointers to the synchronization locking/unlocking functions -- they will be invoked by the library to facilitate atomic transactions. Alternatively, some applications (where possible) might benefit from using a separate heap per thread to avoid the synchronization overhead and reduce contention.

[pavel-kirienko]

@jrahlf thanks! Fixed in #10