Use time/tzdata for timezone in docker

[sapk]

We can remove tzdata of container and use go1.15 in binary timezone.

For details: https://golang.org/doc/go1.15#time/tzdata

[codecov-commenter]

Codecov Report

Merging #12922 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #12922      +/-   ##
==========================================
- Coverage   43.09%   43.07%   -0.02%     
==========================================
  Files         658      658              
  Lines       72454    72454              
==========================================
- Hits        31221    31210      -11     
- Misses      36178    36188      +10     
- Partials     5055     5056       +1     

Impacted Files	Coverage Δ
modules/log/event.go	56.60% <0.00%> (-2.84%)	⬇️
models/unit.go	46.57% <0.00%> (-2.74%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
modules/queue/unique_queue_disk_channel.go	53.84% <0.00%> (-1.54%)	⬇️
services/pull/pull.go	40.78% <0.00%> (-0.50%)	⬇️
modules/util/timer.go	85.71% <0.00%> (+42.85%)	⬆️

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[6543]

any benefits to use build in func?

[sapk]

@6543 it is multiple little improvement:

• no need to download a package (time and data consuming)
• simplify/limit arch different comportement
• less file in image
• should reduce a little the image size

Those are not great improvement but a step forward to remove external binary and file dependency.

[zeripath]

Votes for 1.13? I think it's self-contained so can be merged into 1.13 as we build with 1.15.x

[zeripath]

@sapk if you update I think we can merge this in to 1.13

[techknowlogick]

@sapk can you allow commits from other maintainers to this PR?