Breaking: #24900 - Remove $TYPO3_CONF_VARS[SYS][compat_version] option 

See forge#24900

Description 

The option $TYPO3_CONF_VARS[SYS][compat_version], which was modified on update in the Install Tool wizard, has been removed.

Any checks on GeneralUtility::compat_version are now made against the common constant TYPO3_branch instead of the former TYPO3_CONF_VARS option.

Impact 

Any usage of $TYPO3_CONF_VARS[SYS][compat_version] where the value is different than TYPO3_branch will result in unexpected behaviour.

TypoScript conditions which check for older compat_version will have different behaviour now.

Affected installations 

Any installation where $TYPO3_CONF_VARS[SYS][compat_version] was not set to the currently running version or where the value of compat_version was used to simulate behaviour of an older version. E.g. TypoScript conditions or GeneralUtility::compat_version in extensions.

Migration 

Remove any direct usage of the option, and use the "compat_version" method within GeneralUtility as well as the TypoScript condition "compat_version" which gives more accurate results.