feat: Remove store endpoint

[cleptric]

To move forward on initiatives like https://github.com/getsentry/team-replay/issues/70 and getsentry/team-webplatform-meta#45, we decided to remove the /store endpoint from the Go SDK.

These changes require a self-hosted version of Sentry 20.6.0 or higher. If you are using a version of self-hosted Sentry (aka onpremise) older than 20.6.0 then you will need to upgrade.

I removed quite a few things from logrusentry_test.go.
My reasoning is that we mostly care about testing entryToEvent, as all other functionality is wrapped into CaptureEvent. Making the tests work again would require copying a lot of functionality from client_test.go, something I'm not keen on maintaining.

[tonyo]

Looks good so far

[codecov]

Codecov Report

Patch coverage: 86.66% and project coverage change: -0.21 ⚠️

Comparison is base (f7478f0) 79.86% compared to head (c33e6e5) 79.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #631      +/-   ##
==========================================
- Coverage   79.86%   79.66%   -0.21%     
==========================================
  Files          38       38              
  Lines        3889     3885       -4     
==========================================
- Hits         3106     3095      -11     
- Misses        675      681       +6     
- Partials      108      109       +1     

Impacted Files	Coverage Δ
interfaces.go	92.57% <ø> (ø)
transport.go	78.37% <84.61%> (ø)
dsn.go	96.18% <100.00%> (-0.12%)	⬇️

... and 2 files with indirect coverage changes

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