Remove unnecessary struct2interface dependency (#13929)

* Remove unnecessary struct2interface dependency

Running go mod tidy on the repo removes it.
This was also preventing 1.14beta from running the repo,
because now it verifies modules.txt with go.mod, which had a mismatch.

* fixing CI

* Fix test-server target

* Fix some discrepancies in vendor

* Removing the Makefile target for now

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

vendor/modules.txt

@@ -293,6 +293,9 @@ golang.org/x/image/webp
 # golang.org/x/lint v0.0.0-20191125180803-fdd1cda4f05f
 golang.org/x/lint
 golang.org/x/lint/golint
+# golang.org/x/mod v0.2.0
+golang.org/x/mod/module
+golang.org/x/mod/semver
 # golang.org/x/net v0.0.0-20200114155413-6afb5195e5aa
 golang.org/x/net/bpf
 golang.org/x/net/context
@@ -335,7 +338,7 @@ golang.org/x/text/secure/bidirule
 golang.org/x/text/transform
 golang.org/x/text/unicode/bidi
 golang.org/x/text/unicode/norm
-# golang.org/x/tools v0.0.0-20200207224406-61798d64f025
+# golang.org/x/tools v0.0.0-20200211205636-11eff242d136
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/passes/inspect
 golang.org/x/tools/go/ast/astutil
@@ -351,9 +354,10 @@ golang.org/x/tools/imports
 golang.org/x/tools/internal/fastwalk
 golang.org/x/tools/internal/gopathwalk
 golang.org/x/tools/internal/imports
-golang.org/x/tools/internal/module
 golang.org/x/tools/internal/packagesinternal
-golang.org/x/tools/internal/semver
+# golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
+golang.org/x/xerrors
+golang.org/x/xerrors/internal
 # google.golang.org/genproto v0.0.0-20200128133413-58ce757ed39b
 google.golang.org/genproto/googleapis/rpc/status
 # google.golang.org/grpc v1.26.0