libwebp: Remove unused config.h and libwebp.pri


config.h is only included if HAVE_CONFIG_H is defined, which the
build never does. libwebp.pri is a leftover from the qmake build.

Pick-to: 6.12
Change-Id: I85fbdb83d580321542b773e054c7da7222c5904c
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commitb20fe1b3db702f8e6dd3f2d5f486cdb42a01a707
parent8a6c151950be210f41b41afa8dfb128d15aac53c
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeWed, 30 Sep 2026 07:20:12 +0000