Remove default is plain from occ command help

[paurakhsharma]

Description

This PR removes the default is plain message from occ command help.
Related issue: #33168

After removing the text, the help message looks like this:

[codecov]

Codecov Report

Merging #33169 into master will not change coverage.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master   #33169   +/-   ##
=========================================
  Coverage     64.12%   64.12%           
  Complexity    18720    18720           
=========================================
  Files          1184     1184           
  Lines         70437    70437           
  Branches       1270     1270           
=========================================
  Hits          45171    45171           
  Misses        24896    24896           
  Partials        370      370

Flag	Coverage Δ	Complexity Δ
#javascript	52.89% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.4% <100%> (ø)	18720 <0> (ø)	⬇️

Impacted Files	Coverage Δ	Complexity Δ
core/Command/Base.php	83.6% <100%> (ø)	23 <0> (ø)	⬇️

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[phil-davis]

LGTM
@PVince81 for some occ commands the default output is JSON, so this hardcoded default is plain makes confusion. Please review.

[PVince81]

👍

[PVince81]

backport ?

[phil-davis]

Backport stable10 #33179