Fix incorrect variable documentation (#11127)

In InstallRequiredSystemLibraries the documentation details the
variable CMAKE_SKIP_INSTALL_RULES to skip installation. This
actually doesn't do anything, the variable required is named
CMAKE_INSTALL_SYSTEM_RUNTIME_LIBS_SKIP. This commit amends the
documentation to point to the correct variable.

Modules/InstallRequiredSystemLibraries.cmake

@@ -1,9 +1,9 @@
 # By including this file, all files in the CMAKE_INSTALL_DEBUG_LIBRARIES,
 # will be installed with INSTALL_PROGRAMS into /bin for WIN32 and /lib
-# for non-win32. If CMAKE_SKIP_INSTALL_RULES is set to TRUE before including
-# this file, then the INSTALL command is not called.  The user can use 
-# the variable CMAKE_INSTALL_SYSTEM_RUNTIME_LIBS to use a custom install 
-# command and install them into any directory they want.
+# for non-win32. If CMAKE_INSTALL_SYSTEM_RUNTIME_LIBS_SKIP is set to TRUE
+# before including this file, then the INSTALL command is not called.
+# The user can use the variable CMAKE_INSTALL_SYSTEM_RUNTIME_LIBS to use a
+# custom install command and install them into any directory they want.
 # If it is the MSVC compiler, then the microsoft run
 # time libraries will be found and automatically added to the
 # CMAKE_INSTALL_DEBUG_LIBRARIES, and installed.