Fix release symbols

While refreshing patches for v.2020.5 execution bits were lost for static deltas tests created by patch.
Hence restore correct permission to avoid tests failures for:

• tests/test-delta-ed25519.sh
• tests/test-delta-sign.sh

The libostree-devel.sym should be de-commented in Makefile-libostree.am.
This commit also fixes the 0004-lib-deltas-Add-signature-check-API-for-static-delta-.patch which creates 2 LIBOSTREE_2020.5 entries in libostree-devel.sym.