Fix compiler warnings

Merge from Widevine repo of http://go/wvgerrit/43420

Remove or mark unused variables.  Fix unsigned/signed comparisons.

bug: 73390805
test: unit tests
Change-Id: Ic523400a5decf82fae733042b260e0c39a087cd3

libwvdrmengine/cdm/test/request_license_test.cpp

@@ -42,8 +42,6 @@ namespace {
 
 #define N_ELEM(a) (sizeof(a)/sizeof(a[0]))
 
-const char kPathDelimiter = '/';
-
 // HTTP response codes.
 const int kHttpOk = 200;
 const int kHttpBadRequest = 400;