Merge bitcoin-core/secp256k1#1338: Drop no longer needed `#include ".…

…./include/secp256k1.h"`

e449af6 Drop no longer needed `#include "../include/secp256k1.h"` (Hennadii Stepanov)

Pull request description:

  The removed header includes have not been needed since bitcoin-core/secp256k1#1231.

  Test suggestions:
  1. Using Autottols-based build system:
  ```
  ./autogen.sh
  ./configure
  make clean-precomp
  make
  ```
  2. Using CMake-based build system:
  ```
  cmake -B build -DCMAKE_C_INCLUDE_WHAT_YOU_USE="include-what-you-use"
  cmake --build build --target secp256k1_precomputed
  ```

ACKs for top commit:
  sipa:
    utACK e449af6
  real-or-random:
    utACK e449af6

Tree-SHA512: 5aed7a88e1e03fcc2306c43817712c0652ecf6145679dd17f4719376818d372f619e4180bdaee548f2e82aaccbe6a2ff4c37203121d939af545128c8c48b933e

src/precompute_ecmult.c

@@ -68,7 +68,6 @@ int main(void) {
     fprintf(fp, "/* This file contains an array secp256k1_pre_g with odd multiples of the base point G and\n");
     fprintf(fp, " * an array secp256k1_pre_g_128 with odd multiples of 2^128*G for accelerating the computation of a*P + b*G.\n");
     fprintf(fp, " */\n");
-    fprintf(fp, "#include \"../include/secp256k1.h\"\n");
     fprintf(fp, "#include \"group.h\"\n");
     fprintf(fp, "#include \"ecmult.h\"\n");
     fprintf(fp, "#include \"precomputed_ecmult.h\"\n");

src/precompute_ecmult_gen.c

@@ -33,7 +33,6 @@ int main(int argc, char **argv) {
 
     fprintf(fp, "/* This file was automatically generated by precompute_ecmult_gen. */\n");
     fprintf(fp, "/* See ecmult_gen_impl.h for details about the contents of this file. */\n");
-    fprintf(fp, "#include \"../include/secp256k1.h\"\n");
     fprintf(fp, "#include \"group.h\"\n");
     fprintf(fp, "#include \"ecmult_gen.h\"\n");
     fprintf(fp, "#include \"precomputed_ecmult_gen.h\"\n");

src/precomputed_ecmult.h

@@ -11,6 +11,7 @@
 extern "C" {
 #endif
 
+#include "ecmult.h"
 #include "group.h"
 #if defined(EXHAUSTIVE_TEST_ORDER)
 #    if EXHAUSTIVE_TEST_ORDER == 7