[feat] Remove runtime timings from the default output

[ekouts]

It might be better to remove the runtime timings from the default output, after the conversation in #2415 .
The documentation mentions that these timings correspond only to the ReFrame stages, but it can be misleading for new users that want to use them for performance monitoring.
Normal output:

[----------] start processing checks
[ RUN      ] T0 @generic:default+builtin
[       OK ] ( 1/10) T0 @generic:default+builtin
[ RUN      ] T4 @generic:default+builtin
[       OK ] ( 2/10) T4 @generic:default+builtin

Verbose output:

[----------] start processing checks
[ RUN      ] T0 @generic:default+builtin
[       OK ] ( 1/10) T0 @generic:default+builtin
==> setup: 0.019s compile: 0.035s run: 0.476s sanity: 0.000s performance: 0.000s total: 0.568s
[ RUN      ] T4 @generic:default+builtin
[       OK ] ( 2/10) T4 @generic:default+builtin
==> setup: 0.009s compile: 0.036s run: 0.375s sanity: 0.000s performance: 0.000s total: 0.459s

I still leave them in verbose mode, what do you think @vkarak ? If you agree I will change also all the reframe outputs in the docs.

Closes #2415.

[vkarak]

Should we also close #2415 with this?

[ekouts]

I think so, yes.

[victorusu]

lgtm

[vkarak]

Lgtm, I have a minor comment for improvement.

[codecov-commenter]

Codecov Report

Merging #2425 (b72b7eb) into master (e2843b0) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2425      +/-   ##
==========================================
- Coverage   85.67%   85.66%   -0.01%     
==========================================
  Files          56       56              
  Lines       10466    10460       -6     
==========================================
- Hits         8967     8961       -6     
  Misses       1499     1499              

Impacted Files	Coverage Δ
reframe/frontend/executors/policies.py	92.41% <100.00%> (-0.13%)	⬇️

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