*: remove unnecessary executable permissions

[Luffbee]

What problem does this PR solve?

Some *.go files have executable permission. (Introduced by PR #1902)

What is changed and how it works?

Remove unnecessary executable permissions.

Check List

Tests

• No code

[codecov-io]

Codecov Report

Merging #2095 into master will decrease coverage by 0.43%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2095      +/-   ##
==========================================
- Coverage   77.41%   76.97%   -0.44%     
==========================================
  Files         193      193              
  Lines       19573    19573              
==========================================
- Hits        15152    15067      -85     
- Misses       3317     3369      +52     
- Partials     1104     1137      +33

Impacted Files	Coverage Δ
server/server.go	82.33% <ø> (-2.07%)	⬇️
server/cluster/cluster.go	81.31% <ø> (ø)	⬆️
server/kv/etcd_kv.go	72.72% <0%> (-11.69%)	⬇️
pkg/etcdutil/etcdutil.go	78.26% <0%> (-10.15%)	⬇️
pkg/metricutil/metricutil.go	86.11% <0%> (-8.34%)	⬇️
server/heartbeat_streams.go	67% <0%> (-6%)	⬇️
server/tso/tso.go	77.37% <0%> (-5.84%)	⬇️
server/member/leader.go	76.53% <0%> (-5.62%)	⬇️
server/schedulers/random_merge.go	60.71% <0%> (-3.58%)	⬇️
server/grpc_service.go	56.7% <0%> (-2.82%)	⬇️
... and 9 more

---

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[rleungx]

LGTM

[disksing]

/merge

[sre-bot]

/run-all-tests