delete Gitea specific files that need rewriting for Forgejo

Although it would be possible to modify these files, it would create
conflicts when rebasing. Instead, this commit removes them entirely
and another commit can start from scratch, borrowing content from the
original files.

The drawback of this approach is that some content updates from Gitea
that also need updating in Forgejo will have to be copy/pasted
instead of being merged.

(cherry picked from commit eb85782115f2f453e13561848925760b1abddb16)
(cherry picked from commit 34401f2004445f225a479b8258180f498ac87847)
(cherry picked from commit ef43b1c6910a01a5f9dbd054e23372f6f17f4d9e)
(cherry picked from commit d17fe25e2f915e778eb968c20939dc253f47bcd5)
(cherry picked from commit 3f65dea3e7a5d0983d96d7011385125bd0063ff1)
(cherry picked from commit 3cacb64a1bae713467d3d9b7ebfe626930f2bd35)
(cherry picked from commit b531b014b751233b46e3220c25108fe95531621b)
(cherry picked from commit adf6e7a840c7f7201eddec3ab2b305200b19fc43)
(cherry picked from commit 68c19d977d6aa8e8eb5714f5915b6557379887c0)
(cherry picked from commit 31aa8647ecaf91704652e149fb5d0e891645412d)
(cherry picked from commit be70dd7208c2b40842cb83affa77f6d15ac4d840)
(cherry picked from commit 7f44bb60b16843b0e127a7e5fc89736a1d35d145)
(cherry picked from commit 5098f1224b10ac7b35c1d4c9ece8fbd066a616e8)
(cherry picked from commit dc7a8591442772f9801bfff7a77f1c8806bedb5c)
(cherry picked from commit f1e78dd0067f8d0e9a6ea4dc292ebebdb8b8bcda)
(cherry picked from commit c41ba7a148d1b35df392a7d2af9a52461e1cb217)
(cherry picked from commit f1da66a918a68237894e220d206a5e0251ec85d0)
(cherry picked from commit 99194a3664dc94296f7e1397be45b6fde9e3e718)
(cherry picked from commit 52f356f)
(cherry picked from commit c93ffa72ae35bbdc6cc470823648a1aed0185b5d)
(cherry picked from commit 477c7454d39e813e2bc5107bf84105060acfe743)
(cherry picked from commit 413df23a407547b1a0d480185be9efc388b464eb)

[DOCS] delete Gitea specific files that need rewriting for Forgejo (squash)

(cherry picked from commit df78cedd053e624bcc30b048eac9d6ab10ff5749)
(cherry picked from commit 3b9178b3e5ee1aedff79a6ff5b62fb700f480682)
(cherry picked from commit 9044dcb0e7bb410bbc8a83c8d3610fa6c8355e25)
(cherry picked from commit e138685bacc14138aad46bea2756dc4f6d6b46c0)
(cherry picked from commit 2f1f3fd6b8a7b054bf854ea94ef91c8f87bce996)
(cherry picked from commit 0b47d02df6c93129d825aa1b9d3f481b6cf7f505)
(cherry picked from commit 7625ca6c42b6a333e3a2e25dd3df2744a4180e32)
(cherry picked from commit e0d720a728cf24eaeb1416ac1c5b8de6655ccd44)
(cherry picked from commit 19aa974d120fe5ade8436e5ea0fab6a83f1b9db1)

Author: Loïc Dachary