package/cpp-httplib: remove stale patch

Running the command:

    make cpp-httplib-patch

fails with error:

    Applying 0001-merge-commit-from-fork.patch using patch:
    patching file httplib.h
    Reversed (or previously applied) patch detected!  Skipping patch.
    2 out of 2 hunks ignored -- saving rejects to file httplib.h.rej
    patching file test/test.cc
    Hunk #1 FAILED at 42.
    Hunk #2 FAILED at 2839.
    Hunk #3 FAILED at 3624.
    3 out of 3 hunks FAILED -- saving rejects to file test/test.cc.rej

Commit [1] "package/cpp-httplib: add patch for CVE-2025-46728"
introduced a package patch in the branch next while Buildroot was in
RC cycle. Just after, commit [2] "package/cpp-httplib: bump to
v0.25.0", also in branch next, removed this package patch.

This commit [1] was cherry-picked in [3] in the branch master, to
apply only the security fix for the 2025.08 release.

The merge commit [4] kept the cpp-httplib package patch
"0001-merge-commit-from-fork.patch".

This commit fixes the issue by removing this stale patch.

Fixes:
https://autobuild.buildroot.org/results/5b9843089ade428997035e49817208ce9c09a10e

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/aea7c89396f20570b5ce32c4a235f7011ad0bd01
[2] https://gitlab.com/buildroot.org/buildroot/-/commit/519d03657c6a247f739003a3590c93948e6a48d8
[3] https://gitlab.com/buildroot.org/buildroot/-/commit/fd313c4cebc8c0a8db2ff9641b48e2d8a993c245
[4] https://gitlab.com/buildroot.org/buildroot/-/commit/0af159ae2b0363a90b8c5432cd4cb9bfd3476c5a

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Author: jolivain