tests: refactor: drop secp256k1_ prefix from testrand.h functions

The rename was done with the following command:

$ sed -i 's/secp256k1_testrand/testrand/g' $(git grep -l secp256k1_testrand)

src/testrand.h

@@ -12,37 +12,37 @@
 /* A non-cryptographic RNG used only for test infrastructure. */
 
 /** Seed the pseudorandom number generator for testing. */
-SECP256K1_INLINE static void secp256k1_testrand_seed(const unsigned char *seed16);
+SECP256K1_INLINE static void testrand_seed(const unsigned char *seed16);
 
 /** Generate a pseudorandom number in the range [0..2**32-1]. */
-SECP256K1_INLINE static uint32_t secp256k1_testrand32(void);
+SECP256K1_INLINE static uint32_t testrand32(void);
 
 /** Generate a pseudorandom number in the range [0..2**64-1]. */
-SECP256K1_INLINE static uint64_t secp256k1_testrand64(void);
+SECP256K1_INLINE static uint64_t testrand64(void);
 
 /** Generate a pseudorandom number in the range [0..2**bits-1]. Bits must be 1 or
  *  more. */
-SECP256K1_INLINE static uint64_t secp256k1_testrand_bits(int bits);
+SECP256K1_INLINE static uint64_t testrand_bits(int bits);
 
 /** Generate a pseudorandom number in the range [0..range-1]. */
-static uint32_t secp256k1_testrand_int(uint32_t range);
+static uint32_t testrand_int(uint32_t range);
 
 /** Generate a pseudorandom 32-byte array. */
-static void secp256k1_testrand256(unsigned char *b32);
+static void testrand256(unsigned char *b32);
 
 /** Generate a pseudorandom 32-byte array with long sequences of zero and one bits. */
-static void secp256k1_testrand256_test(unsigned char *b32);
+static void testrand256_test(unsigned char *b32);
 
 /** Generate pseudorandom bytes with long sequences of zero and one bits. */
-static void secp256k1_testrand_bytes_test(unsigned char *bytes, size_t len);
+static void testrand_bytes_test(unsigned char *bytes, size_t len);
 
 /** Flip a single random bit in a byte array */
-static void secp256k1_testrand_flip(unsigned char *b, size_t len);
+static void testrand_flip(unsigned char *b, size_t len);
 
 /** Initialize the test RNG using (hex encoded) array up to 16 bytes, or randomly if hexseed is NULL. */
-static void secp256k1_testrand_init(const char* hexseed);
+static void testrand_init(const char* hexseed);
 
 /** Print final test information. */
-static void secp256k1_testrand_finish(void);
+static void testrand_finish(void);
 
 #endif /* SECP256K1_TESTRAND_H */