cmake: Remove FindRSSDK

Follow-up to PR #7371 (commit a1a98f9cfd15f4c74cf15ddf4ef65ca6058016de).

We forgot to remove the Finder that was only used for that plugin. Let's
remove it now.

cmake/Modules/FindRSSDK.cmake

@@ -1,49 +0,0 @@
-# Once done these will be defined:
-#
-# RSSDK_FOUND RSSDK_INCLUDE_DIRS RSSDK_LIBRARIES
-#
-# For use in OBS:
-#
-# RSSDK_INCLUDE_DIR
-
-if(CMAKE_SIZEOF_VOID_P EQUAL 8)
-  set(_RSSDK_lib_dir "x64")
-else()
-  set(_RSSDK_lib_dir "Win32")
-endif()
-
-find_path(
-  RSSDK_INCLUDE_DIR
-  NAMES pxcsession.h
-  HINTS ENV RSSDK_DIR
-  PATH_SUFFIXES include)
-
-find_library(
-  RSSDK_LIB
-  NAMES libpxc
-  HINTS ENV RSSDK_DIR
-  PATH_SUFFIXES lib/${_RSSDK_lib_dir})
-
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(RSSDK DEFAULT_MSG RSSDK_LIB RSSDK_INCLUDE_DIR)
-mark_as_advanced(RSSDK_INCLUDE_DIR RSSDK_LIB)
-
-if(RSSDK_FOUND)
-  set(RSSDK_INCLUDE_DIRS ${RSSDK_INCLUDE_DIR})
-  set(RSSDK_LIBRARIES ${RSSDK_LIB})
-
-  if(NOT TARGET RSS::SDK)
-    if(IS_ABSOLUTE "${RSSDK_LIBRARIES}")
-      add_library(RSS:SDK UNKNOWN IMPORTED)
-      set_target_properties(RSS:SDK PROPERTIES IMPORTED_LOCATION
-                                               "${RSSDK_LIBRARIES}")
-    else()
-      add_library(RSS:SDK INTERFACE IMPORTED)
-      set_target_properties(RSS:SDK PROPERTIES IMPORTED_LIBNAME
-                                               "${RSSDK_LIBRARIES}")
-    endif()
-
-    set_target_properties(RSS:SDK PROPERTIES INTERFACE_INCLUDE_DIRECTORIES
-                                             "${RSSDK_INCLUDE_DIRS}")
-  endif()
-endif()