Remove unused secp256k1_fe_inv_all_var #878

1. 
   sipa commented at 4:18 am on January 24, 2021: contributor

   This function is only used in tests, since its functionality was inlined into secp256k1_ge_set_all_gej_var in #553.

   Closes #873.

2. Remove unused secp256k1_fe_inv_all_var 75d2ae149e
3. sipa cross-referenced this on Jan 24, 2021 from issue UB in tests: Invalid pointer comparison in secp256k1_fe_inv_all_var by practicalswift
4. 
   gmaxwell commented at 6:24 am on January 24, 2021: contributor

   LGTM.
5. 
   practicalswift commented at 7:49 am on January 24, 2021: contributor

   cr ACK 75d2ae149ef37d3aa42fdefd1529aad89859816c: patch looks correct
6. 
   real-or-random commented at 5:55 pm on January 24, 2021: contributor

   utACK https://github.com/bitcoin-core/secp256k1/commit/75d2ae149ef37d3aa42fdefd1529aad89859816c @practicalswift What’s a “cr ACK”? ah “code review”?
7. 
   jonasnick commented at 1:39 pm on January 25, 2021: contributor

   utACK 75d2ae149ef37d3aa42fdefd1529aad89859816c
8. jonasnick merged this on Jan 25, 2021
9. jonasnick closed this on Jan 25, 2021

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10. sipa cross-referenced this on Jan 25, 2021 from issue Safegcd inverses, drop Jacobi symbols, remove libgmp by sipa
11. Fabcien referenced this in commit c47149e07c on Apr 8, 2021
12. deadalnix referenced this in commit 40fe4ade67 on Apr 9, 2021

Contributors
sipa gmaxwell practicalswift real-or-random jonasnick