Clean up for BigInteger

[GitHubPang]

• There were 2 occurrences of "subtraction" in the same sentence, so I removed one.
• The sentence mentioned "negation" and "unary negation" which are equivalent (since negation is always unary), so I removed one.

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Issue Details

---

• There were 2 occurrences of "subtraction" in the same sentence, so I removed one.
• The sentence mentioned "negation" and "unary negation" which are equivalent (since negation is always unary), so I removed one.

Author:	GitHubPang
Assignees:	-
Labels:	area-System.Numerics
Milestone:	-

[opbld31]

Docs Build status updates of commit b4be34c:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Numerics/BigInteger.xml	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

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[BillWagner]

Thanks again @GitHubPang

I'll now.