remove 'pipeline ci' commands from doc frontpage (it's now deprecated)

[meleu]

Description

Just removing from the documentation frontpage the glab pipeline ci commands. They are now deprecated.

Related Issue

https://github.com/profclems/glab/issues/372

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation
• [ ] Chore (Related to CI or Packaging to platforms)

[codecov[bot]]

Codecov Report

Merging #996 (06d7d91) into trunk (f405b97) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##            trunk     #996   +/-   ##
=======================================
  Coverage   59.59%   59.59%           
=======================================
  Files          98       98           
  Lines        7707     7707           
=======================================
  Hits         4593     4593           
  Misses       2704     2704           
  Partials      410      410           

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