Remove deprecated runner set up instruction

What does this MR do?

As we are not supporting 1-click apps installation on the Kubernetes cluster anymore, the instruction to install GitLab Runner automatically is deprecated. The aim of this MR is to remove unnecessary instruction from the Settings -> CI/CD page both for the project and group level.

Together with these changes small UI adjustments are introduced:

1. The page on the group level hasn't supported the fixed layout that seems inconsistent with the same page on the project level. Added the fixed layout support.
2. Changed the subtitle of the Group Runners section to look similar to the Specific Runners and Shared runners sections.

Screenshots or Screencasts (strongly suggested)

Project level view:

Before	After

Group level view:

Before	After

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• [-] I have added/updated documentation, or it's not needed. (Is documentation required?)
• [-] I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• [-] I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• [-] I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #336229 (closed)