If you want completely delete revisions from the history between other revisions and don't want the revisions from shift upon dump loading like:
------- Committed new rev 1 (loaded from original rev 2) >>>
...
------- Committed new rev 2 (loaded from original rev 3) >>>
...
Then you can just replace all blobs in the dump for each revision <N> from:
Revision-number: <N>
... <blob> ...
to:
Revision-number: <N>
or
Revision-number: <N>
Prop-content-length: 0
Content-length: 0
But to make it compatible, for example, with
https://sourceforge.net/p/PROJECT/REPO/commit_browser UI (otherwise it will stuck on loading):
Revision-number: <N>
Prop-content-length: 56
Content-length: 56
K 8
svn:date
V 27
1970-01-01T00:00:00.000000Z
PROPS-END
This will leave all these revisions as empty and other revisions on the same places upon dump loading.
The TortoiseSVN GUI show log will show them as (none).