Fix -Wunused-but-set-variable clang warning to unblock an upcoming crosstool release.

Removed offset variable as it was initialised to 0 and incremented slowly but not used anywhere.

Tested:
- before: http://sponge2/e8af26ad-1bc7-4426-9abc-f10ff8fc0678
- after: http://sponge2/87824287-2a55-4439-8d3a-c915249e8eae
PiperOrigin-RevId: 438011277
diff --git a/quic/core/quic_version_manager_test.cc b/quic/core/quic_version_manager_test.cc
index da87c4a..cc45cd4 100644
--- a/quic/core/quic_version_manager_test.cc
+++ b/quic/core/quic_version_manager_test.cc
@@ -41,7 +41,6 @@
   EXPECT_THAT(manager.GetSupportedAlpns(),
               ElementsAre("h3-Q050", "h3-Q046", "h3-Q043"));
 
-  int offset = 0;
   QuicEnableVersion(ParsedQuicVersion::Draft29());
   expected_parsed_versions.insert(expected_parsed_versions.begin(),
                                   ParsedQuicVersion::Draft29());
@@ -54,7 +53,6 @@
   EXPECT_THAT(manager.GetSupportedAlpns(),
               ElementsAre("h3-29", "h3-Q050", "h3-Q046", "h3-Q043"));
 
-  offset++;
   QuicEnableVersion(ParsedQuicVersion::RFCv1());
   expected_parsed_versions.insert(expected_parsed_versions.begin(),
                                   ParsedQuicVersion::RFCv1());
@@ -67,7 +65,6 @@
   EXPECT_THAT(manager.GetSupportedAlpns(),
               ElementsAre("h3", "h3-29", "h3-Q050", "h3-Q046", "h3-Q043"));
 
-  offset++;
   QuicEnableVersion(ParsedQuicVersion::V2Draft01());
   expected_parsed_versions.insert(expected_parsed_versions.begin(),
                                   ParsedQuicVersion::V2Draft01());