util/cbmem: Fix test case 3 compilation

Removed unused variable

repos/apache-mynewt-core/util/cbmem/selftest/src/testcases/
    cbmem_test_case_3.c:29:9: error: variable 'i' set but not
    used [-Werror,-Wunused-but-set-variable]
4941
    int i;
4942
        ^
4943
1 error generated.

util/cbmem/selftest/src/testcases/cbmem_test_case_3.c

@@ -26,10 +26,8 @@ TEST_CASE_SELF(cbmem_test_case_3)
     uint16_t off;
     uint16_t len;
     uint8_t buf[128];
-    int i;
     int rc;
 
-    i = 0;
     cbmem_iter_start(&cbmem1, &iter);
     while (1) {
         hdr = cbmem_iter_next(&cbmem1, &iter);
@@ -54,7 +52,6 @@ TEST_CASE_SELF(cbmem_test_case_3)
         TEST_ASSERT_FATAL(len == CBMEM1_ENTRY_SIZE,
                 "Couldn't read full entry, expected %d got %d",
                 CBMEM1_ENTRY_SIZE, len);
-        i++;
 
         /* go apesh*t, and read data out of bounds, see what we get. */
         rc = cbmem_read(&cbmem1, hdr, buf, CBMEM1_ENTRY_SIZE * 2, sizeof(buf));