Remove redundant declarations of MIN

Apparently somewhere along the line we decided that MIN might be
missing.

But we already defined it (if it was missing) in compat.h, which
everybody includes.

Closes ticket 18889.

changes/bug18889

@@ -0,0 +1,2 @@
+  o Code simplification and refactoring:
+    - Remove redundant declarations of the MIN macro. Closes ticket 18889.

src/common/crypto.c

@@ -2384,8 +2384,6 @@ tor_check_dh_key(int severity, BIGNUM *bn)
   return -1;
 }
 
-#undef MIN
-#define MIN(a,b) ((a)<(b)?(a):(b))
 /** Given a DH key exchange object, and our peer's value of g^y (as a
  * <b>pubkey_len</b>-byte value in <b>pubkey</b>) generate
  * <b>secret_bytes_out</b> bytes of shared key material and write them

src/or/circuitbuild.c

@@ -47,10 +47,6 @@
 #include "routerset.h"
 #include "crypto.h"
 
-#ifndef MIN
-#define MIN(a,b) ((a)<(b)?(a):(b))
-#endif
-
 static channel_t * channel_connect_for_circuit(const tor_addr_t *addr,
                                                uint16_t port,
                                                const char *id_digest);

src/test/test-memwipe.c

@@ -6,9 +6,6 @@
 #include "crypto.h"
 #include "compat.h"
 
-#undef MIN
-#define MIN(a,b) ( ((a)<(b)) ? (a) : (b) )
-
 static unsigned fill_a_buffer_memset(void) __attribute__((noinline));
 static unsigned fill_a_buffer_memwipe(void) __attribute__((noinline));
 static unsigned fill_a_buffer_nothing(void) __attribute__((noinline));