chore: remove redundant po2json dev dependency

[villebro]

SUMMARY

While checking licenses with license-checker on superset-frontend, I noticed we have an LGPL licensed dev dependency po2json, which is not compliant with Apache license policies. Since po2json package is not being used in either CI or npm scripts, and is only referred to in the contributing guide where users are instructed to globally install the package when translating JS files, the package isn't really needed as a dev dependency.

AFTER

The list doesn't contain any (L)GPL licensed packages:

$ license-checker --summary
├─ MIT: 2076
├─ ISC: 159
├─ BSD-3-Clause: 95
├─ Apache-2.0: 89
├─ BSD-2-Clause: 57
├─ MIT*: 6
├─ CC0-1.0: 5
├─ BSD*: 4
├─ BSD: 4
├─ Unlicense: 3
├─ 0BSD: 3
├─ (MIT OR CC0-1.0): 3
├─ CC-BY-4.0: 2
├─ WTFPL: 2
├─ Custom: https://github.com/tmcw/jsonlint: 1
├─ (Unlicense OR Apache-2.0): 1
├─ (MIT OR Apache-2.0): 1
├─ MPL-2.0: 1
├─ Custom: https://github.com/saikocat/colorbrewer.: 1
├─ Apache-Style: 1
├─ (MPL-2.0 OR Apache-2.0): 1
├─ Apache*: 1
├─ AFLv2.1,BSD: 1
├─ ODC-By-1.0: 1
├─ Apache-2.0 WITH LLVM-exception: 1
├─ (BSD-3-Clause OR GPL-2.0): 1
├─ (WTFPL OR MIT): 1
├─ (MIT AND Zlib): 1
├─ (MIT AND BSD-3-Clause): 1
├─ CC-BY-3.0: 1
├─ (MIT OR GPL-3.0): 1
└─ Public Domain: 1

BEFORE

See the reference to "GNU Library General Public License":

$ license-checker --summary
├─ MIT: 2082
├─ ISC: 159
├─ BSD-3-Clause: 95
├─ Apache-2.0: 89
├─ BSD-2-Clause: 57
├─ MIT*: 7
├─ CC0-1.0: 5
├─ BSD*: 4
├─ BSD: 4
├─ Unlicense: 3
├─ 0BSD: 3
├─ (MIT OR CC0-1.0): 3
├─ CC-BY-4.0: 2
├─ WTFPL: 2
├─ Custom: https://github.com/tmcw/jsonlint: 1
├─ (Unlicense OR Apache-2.0): 1
├─ (MIT OR Apache-2.0): 1
├─ MPL-2.0: 1
├─ Custom: https://github.com/saikocat/colorbrewer.: 1
├─ Apache-Style: 1
├─ (MPL-2.0 OR Apache-2.0): 1
├─ Apache*: 1
├─ AFLv2.1,BSD: 1
├─ ODC-By-1.0: 1
├─ Apache-2.0 WITH LLVM-exception: 1
├─ (BSD-3-Clause OR GPL-2.0): 1
├─ (WTFPL OR MIT): 1
├─ (MIT AND Zlib): 1
├─ GNU Library General Public License: 1
├─ (MIT AND BSD-3-Clause): 1
├─ CC-BY-3.0: 1
├─ (MIT OR GPL-3.0): 1
└─ Public Domain: 1

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[amitmiran137]

LGTM!

[codecov]

Codecov Report

Merging #17129 (c3dd2f4) into master (c9c669d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #17129   +/-   ##
=======================================
  Coverage   76.94%   76.94%           
=======================================
  Files        1031     1031           
  Lines       55213    55213           
  Branches     7507     7507           
=======================================
  Hits        42483    42483           
  Misses      12480    12480           
  Partials      250      250           

Flag	Coverage Δ
javascript	70.92% <ø> (ø)

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[kgabryje]

Double checked to verify it's not used anywhere - no occurences in superset, superset-ui nor superset-ui-plugins-deckgl. LGTM