KNOWN_BUGS: remove fixed or outdated issues, move non-bugs

- remove h3 issues believed to be fixed

- make the flaky CI issue be generic and not Windows specific

- "TLS session cache does not work with TFO" now documented

  This is now a documented restriction and not a bug. TFO in general is
  rarely used and has other problems, making it a low-priotity thing to
  work on.

- remove "Renegotiate from server may cause hang for OpenSSL backend"

  This is an OpenSSL issue, not a curl one. Even if it taints curl.

- rm "make distclean loops forever"

- rm "configure finding libs in wrong directory"

  Added a section to docs/INSTALL.md about it.

- "A shared connection cache is not thread-safe"

  Moved over to TODO and expanded for other sharing improvements we
  could do

- rm "CURLOPT_OPENSOCKETPAIRFUNCTION is missing"

- rm "Blocking socket operations in non-blocking API"

  Already listed as a TODO

- rm "curl compiled on OSX 10.13 failed to run on OSX 10.10"

  Water under the bridge. No one cares about this anymore.

- rm "build on Linux links libcurl to libdl"

  Verified to not be true (anymore).

- rm "libpsl is not supported"

  The cmake build supports it since cafb356e19

Closes #10963

docs/INSTALL.md

@@ -149,6 +149,18 @@ conflicting identical symbol names.
 When you build with multiple TLS backends, you can select the active one at
 run-time when curl starts up.
 
+## configure finding libs in wrong directory
+
+When the configure script checks for third-party libraries, it adds those
+directories to the `LDFLAGS` variable and then tries linking to see if it
+works. When successful, the found directory is kept in the `LDFLAGS` variable
+when the script continues to execute and do more tests and possibly check for
+more libraries.
+
+This can make subsequent checks for libraries wrongly detect another
+installation in a directory that was previously added to `LDFLAGS` by another
+library check.
+
 # Windows
 
 ## Building Windows DLLs and C runtime (CRT) linkage issues