fix: resolve another compiler warning

```console
In file included from /root/project/test/test.c:4:
/root/project/test/../dist/postject-api.h: In function 'postject_find_resource':
/root/project/test/../dist/postject-api.h:96:9: error: unused variable 'ptr' [-Werror=unused-variable]
   96 |   void* ptr = NULL;
      |         ^~~
cc1: all warnings being treated as errors
```

Refs: https://app.circleci.com/pipelines/github/postmanlabs/postject/180/workflows/d0eb47c0-5482-4c85-9c63-aa854ddb0221/jobs/1398?invite=true#step-110-678
Signed-off-by: Darshan Sen <raisinten@gmail.com>

postject-api.h

@@ -93,7 +93,6 @@ static const void* postject_find_resource(
 
   return ptr;
 #elif defined(__linux__)
-  void* ptr = NULL;
 
   if (options != NULL && options->elf_section_name != NULL) {
     name = options->elf_section_name;