Change a couple of comments to use "SQLITE_MUTEX_OMIT" instead of OMIT_MUTEX.

FossilOrigin-Name: b733e939f785111eac987fe4a25ccfa512e4f0b4

src/mutex.c

@@ -150,4 +150,4 @@ int sqlite3_mutex_notheld(sqlite3_mutex *p){
 }
 #endif
 
-#endif /* SQLITE_OMIT_MUTEX */
+#endif /* SQLITE_MUTEX_OMIT */

src/mutex.h

@@ -70,4 +70,4 @@
 #define sqlite3MutexAlloc(X)      ((sqlite3_mutex*)8)
 #define sqlite3MutexInit()        SQLITE_OK
 #define sqlite3MutexEnd()
-#endif /* defined(SQLITE_OMIT_MUTEX) */
+#endif /* defined(SQLITE_MUTEX_OMIT) */