Get rid of secp256k1_fe_const_b #1283

1. 
   sipa commented at 8:10 pm on April 20, 2023: contributor

   Replaces #1282.

   Its only remaining use is in a test introduced in #1118, and it is easily replaced by the new secp256k1_fe_add_int from #1217.

2. Get rid of secp256k1_fe_const_b 69e1ec0331
3. sipa cross-referenced this on Apr 20, 2023 from issue Remove secp256k1_fe_const_b by roconnor-blockstream
4. real-or-random approved
5. 
   real-or-random commented at 8:09 am on April 21, 2023: contributor

   utACK 69e1ec033120497b83dd95d92166fa05c54b8a06
6. real-or-random merged this on Apr 21, 2023
7. real-or-random closed this on Apr 21, 2023

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8. sipa referenced this in commit b4eb644b6c on May 12, 2023
9. hebasto referenced this in commit 49c52ea2b1 on May 13, 2023
10. vmta referenced this in commit e1120c94a1 on Jun 4, 2023
11. sipa referenced this in commit 901336eee7 on Jun 21, 2023
12. vmta referenced this in commit 8f03457eed on Jul 1, 2023
13. jonasnick cross-referenced this on Jul 24, 2023 from issue Upstream PRs 1268, 1276, 1267, 1265, 1230, 1279, 1273, 1263, 1231, 1285, 1283, 1205, 1286, 1275, 1234, 1239, 1240, 1284, 1277, 1289, 1270, 1296, 1301, 1299, 1066, 1300, 1292, 1305, 1303, 1133, 1306, 1207, 1304, 1307, 1311, 1309, 1312 by jonasnick

Contributors
sipa real-or-random