remove confusing explanation about reusing nonce in counter mode docs
remove confusing explanation about reusing nonce in counter mode docs

Hasimir/cryptography,dstufft/cryptography,sholsapp/cryptography,kimvais/cryptography,Ayrx/cryptography,Lukasa/cryptography,dstufft/cryptography,Hasimir/cryptography,Hasimir/cryptography,dstufft/cryptography,Ayrx/cryptography,Lukasa/cryptography,sholsapp/cryptography,dstufft/cryptography,Hasimir/cryptography,sholsapp/cryptography,glyph/cryptography,kimvais/cryptography,skeuomorf/cryptography,dstufft/cryptography,skeuomorf/cryptography,Ayrx/cryptography,Ayrx/cryptography,bwhmather/cryptography,sholsapp/cryptography,glyph/cryptography,kimvais/cryptography,kimvais/cryptography,bwhmather/cryptography,skeuomorf/cryptography,skeuomorf/cryptography,bwhmather/cryptography,bwhmather/cryptography,Lukasa/cryptography