Don't use templating to allow for dead-code elimination

[marckhouzam]

What this PR does / why we need it

This change has no visible effect to the behaviour of plugins, except for allowing them to possibly reduce their binary size.

When templating is used, the linker cannot know which functions are called and which ones are not; this is because templating uses calls to MethodByName() which can be used to call any function (similar to reflection).

With the release of Cobra 1.9.1, templates are no longer used by default in Cobra. By also not using templates in the tanzu-plugin-runtime it now gives an opportunity for plugins to try to avoid templates to allow dead-code elimination to work, if they so choose.

This PR therefore removes the use of templates in tanzu-plugin-runtime.
Note that we had technically already moved to using go code instead of templates but we had just kept the template engine calling the go code.

Note that the new TestDeadcodeElimination test is meant to notify us if templates are added. However, if any new dependency used by tanzu-plugin-runtime uses templates or reflection, it would also turn off dead-code elimination and fail the test. If there is a justification for that to happen, we will just need to remove the test.

Ref: spf13/cobra#1956

Which issue(s) this PR fixes

Fixes # N/A

Describe testing done for PR

I built a plugin using this new PR and verified that both its usage and help printouts were not changed:

$ tz project list -h
List the projects in the current workspace.

Project list configuration options include:
- Output the project formatted

Usage:
  tanzu project list [flags]

Aliases:
  list, ls

Examples:
  tanzu project list
  tanzu project list --wide

Flags:
  -h, --help   help for list
  -w, --wide   output the project list with additional information
$ tz project list --invalid
Usage:
  tanzu project list [flags]

Aliases:
  list, ls

Examples:
  tanzu project list
  tanzu project list --wide

Flags:
  -h, --help   help for list
  -w, --wide   output the project list with additional information

Error: unknown flag: --invalid

Release note

Do not use templates so that dead-code elimination is not turned off.

Additional information

Special notes for your reviewer

[prkalle]

Nice changes!!

LGTM. Thanks!