make the upper limit of allocated atoms and pairs hard coded

[arvidn]

Now that the 1.8.0 soft-fork has activated, all blocks are validated with these limits. Hard coding the limit opens up the ability to use some of the bits in NodePtr to encode the category of the node, for instance.

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 7432500517

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 93.805%

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Totals
Change from base Build 7279846177:	0.001%
Covered Lines:	5406
Relevant Lines:	5763

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💛 - Coveralls