Remove unused http fallback code

[Anton-Kalpakchiev]

During Kraken's migration from HTTP to HTTPS, a mechanism was needed to fallback to HTTP if HTTPS failed for some reason. This migration has been finished for years, but the unused fallback code stayed. This PR cleans it up, resulting in less code to maintain and lower overall complexity.

[gkeesh7]

While Kraken's migration from HTTP to HTTPS did introduce a fallback mechanism to HTTP for failed HTTPS attempts, I don’t believe this code is unused. It actually aids in quickly unit testing the codebase without needing to configure TLS settings explicitly for HTTPS connections. Additionally, I suspect the failing builds on this PR might be due to the removal of a fix that was included in a previous PR.

[gkeesh7]

--- FAIL: TestTagDownloadSuccess (0.00s)
    tagclient_test.go:66: 
                Error Trace:    tagclient_test.go:66
                Error:          Received unexpected error:
                                check blob exists: network error: Head "https://127.0.0.1:38263/v2/namespace-foo/repo-bar/manifests/nL8h8bE8": http: server gave HTTP response to HTTPS client
                Test:           TestTagDownloadSuccess
--- FAIL: TestTagDownloadFileNotFound (0.00s)
    tagclient_test.go:96: 
                Error Trace:    tagclient_test.go:96
                Error:          Not equal: 
                                expected: &errors.errorString{s:"blob not found"}
                                actual  : &errors.errorString{s:"check blob exists: network error: Head \"https://127.0.0.1:39683/v2/namespace-foo/repo-bar/manifests/wLjt8IvG\": http: server gave HTTP response to HTTPS client"}
                            
                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1,3 +1,3 @@
                                 (*errors.errorString)({
                                - s: (string) (len=14) "blob not found"
                                + s: (string) (len=158) "check blob exists: network error: Head \"https://127.0.0.1:39683/v2/namespace-foo/repo-bar/manifests/wLjt8IvG\": http: server gave HTTP response to HTTPS client"
                                 })
                Test:           TestTagDownloadFileNotFound