Remove compatibility with PHP 7.3

[jordisala1991]

Subject

I am targeting this branch, because this is BC.

[jordisala1991]

this is problematic, since we add rector and upgrade the code for php 7.4, but the composer.json still showed us 7.3, there was not a build with 7.3 but we didn't notice until someone opened a PR againts SonataAdminBundle 3.x, which supports php 7.3:
sonata-project/SonataAdminBundle#7818

[VincentLanglet]

this is problematic, since we add rector and upgrade the code for php 7.4, but the composer.json still showed us 7.3, there was not a build with 7.3 but we didn't notice until someone opened a PR againts SonataAdminBundle 3.x, which supports php 7.3: sonata-project/SonataAdminBundle#7818

Indeed the 1.14 and 1.15 will create an issue with php 7.3...

What should we do ? The only idea I have so far is

• Starting a branch from 1.14.0
• Reverting the rector changes
• Releasing this as 1.14.1
• Starting a branch from 1.15.0
• Reverting the rector changes
• Releasing this as 1.15.1

WDYT @jordisala1991 ?

(Or doing this for 1.15.0 might be enough)

[VincentLanglet]

We can do a 1.15.1 release from the #341 branch (without merging) in order to fix the 7.3 compatibility. @jordisala1991