refactor(core): Remove references to watcher and delete it

[timoffex]

Description

Finishes replacing watcher by watcher2.

[codecov]

Codecov Report

Attention: Patch coverage is 16.27907% with 36 lines in your changes are missing coverage. Please review.

Project coverage is 75.82%. Comparing base (f6ca1ac) to head (fe14225).

Additional details and impacted files

@@                                              Coverage Diff                                              @@
##           spr/timoffex/main.refactorcore-remove-references-to-watcher-and-delete-it    #7599      +/-   ##
=============================================================================================================
+ Coverage                                                                      75.78%   75.82%   +0.03%     
=============================================================================================================
  Files                                                                            502      499       -3     
  Lines                                                                          54016    53900     -116     
=============================================================================================================
- Hits                                                                           40938    40870      -68     
+ Misses                                                                         12663    12628      -35     
+ Partials                                                                         415      402      -13     

Flag	Coverage Δ
func	41.18% <ø> (ø)
system	63.48% <16.27%> (+0.12%)	⬆️
unit	56.38% <13.95%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
core/internal/runfiles/uploader.go	78.94% <ø> (-0.13%)	⬇️
core/pkg/server/sender.go	70.94% <100.00%> (+0.07%)	⬆️
core/pkg/server/stream.go	97.02% <100.00%> (-0.02%)	⬇️
core/pkg/server/stream_init.go	94.80% <100.00%> (ø)
core/pkg/server/tb.go	22.41% <0.00%> (+1.10%)	⬆️

... and 5 files with indirect coverage changes

[kptkin]

nice. will you be renaming watcher2 to watcher (or some other name that doesn't have the 2 suffix :))?