Revert "Issue #3038365 by acbramley, Grimreaper, smustgrave, catch: Add owner to the BlockContent entity type"

This reverts commit b8d5c0e4.

Issue #3038365 by acbramley, Grimreaper, smustgrave, catch: Add owner to the BlockContent entity type

Issue #3397493 by borisson_, phenaproxima, Wim Leers: Add validation constraints to block_content.type.*

Issue #3318549 by smustgrave, mstrelan, larowlan, rkoller, AaronMcHale, acbramley: Rename Custom Block terminology in the admin UI

Issue #1975064 by smustgrave, tanc, ravi.shankar, seanpclark, pixlkat, wengerk, meena.bisht, cboyden, rjg, klaasvw, nikitagupta, larowlan, MaskOta, mlncn, dsnopek, fenstrat, fago, vacho, yobottehg, Grimreaper, rpayanm, B-Prod, SKAUGHT, rkoller, yoroy, stefan.r, psf_, AaronMcHale, rootwork, ifrik, TravisCarden, stella, kae76, josephdpurcell@gmail.com, eelkeblok, andypost, benjifisher: Add more granular block permissions

Issue #2862564 by smustgrave, Manuel Garcia, ifrik, acbramley, amjad1233, benjifisher, manuel.adan, Anchal_gupta, tedbow, Lendude, yogeshmpawar, larowlan, rkoller, AaronMcHale, gambry, rachel_norfolk, yoroy, xjm, Webbeh, catch, mstrelan: Move Custom block library to Content

Issue #3053881 by Luke.Leber, bkosborne, tyler-paavola, Sam152, Rishi Kulshreshtha, Odai Atieh, chrisolof, acbramley, ethomas08, Oscaner, kyberman, aarti zikre, joshua1234511, larowlan, catch: Reverting entity revisions that contain custom blocks erroneously triggers EntityChangedConstraint

Issue #3106666 by catch, jungle, xjm, alexpott, tim.plunkett, Berdir: Remove post updates added prior to 8.8.0

Issue #3065663 by phenaproxima, alexpott, amateescu, tim.plunkett, Wim Leers: Several post-update functions try to update config entity types without checking if they exist

Issue #2988435 by effulgentsia, tedbow, penyaskito, tim.plunkett: block_content_post_update_add_views_reusable_filter uses an string instead of int for "group"

Issue #2976334 by tedbow, Wim Leers, johndevman, tim.plunkett, amateescu, phenaproxima, larowlan, Berdir, EclipseGc, samuel.mortenson, johnzzon: Allow Custom blocks to be set as non-reusable adding access restriction based on where it was used

Issue #2976334 by tedbow, Wim Leers, johndevman, tim.plunkett, phenaproxima, larowlan, samuel.mortenson, Berdir, EclipseGc, johnzzon: Allow Custom blocks to be set as non-reusable adding access restriction based on where it was used