[TASK] Remove leftovers of lib.stdheader

Since the removal of css_styled_content the TypoScript snippet
`lib.stdheader` is gone. This patch removes some leftovers in the
`addPItoST43` method and some other places.

Resolves: #98012
Related: #80876
Releases: main
Change-Id: I3e1b2795c05b464f4210abc0968f507f20f9fba7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75273
Tested-by: core-ci <[email protected]>
Tested-by: Stefan Bürk <[email protected]>
Tested-by: Christian Kuhn <[email protected]>
Tested-by: Benni Mack <[email protected]>
Reviewed-by: Stefan Bürk <[email protected]>
Reviewed-by: Christian Kuhn <[email protected]>
Reviewed-by: Benni Mack <[email protected]>

Author: nhovratov

Resources/Public/JavaScript/Mode/typoscript/typoscript.js

@@ -774,7 +774,6 @@
         'splitChar': kw('splitChar'),
         'splitRendering': kw('splitRendering'),
         'src': kw('src'),
-        'stdheader': kw('stdheader'),
         'stdWrap': A,
         'stdWrap2': kw('stdWrap2'),
         'strftime': kw('strftime'),