Remove GODEBUG

[nsurfer]

After updating to a newer version of Go, GODEBUG=x509sha1=1 is necessary for this test to pass.

2022/08/02 16:38:00 http: TLS handshake error from 127.0.0.1:54874: remote error: tls: bad certificate
    exporter_test.go:187: Received TLS error:  error from get: Get "https://127.0.0.1:37483/metrics": x509: certificate signed by unknown authority (possibly because of "x509: cannot verify signature: insecure algorithm SHA1-RSA (temporarily override with GODEBUG=x509sha1=1)" while trying to verify candidate authority certificate "localhost")
--- FAIL: TestExporterHTTPS (0.05s)

We need to update the TLS certificates so they don't use SHA1-RSA and then remove GODEBUG=x509sha1=1 from the Makefile.