CMake: Remove documentation for -E build (#12446)

The '-E build build_dir' command was created and documented, but then
morphed into '--build build_dir' instead, ... and then the -E documentation
was never removed. This commit fixes that oversight.

Source/cmake.cxx

@@ -1112,7 +1112,6 @@ void CMakeCommandUsage(const char* program)
   errorStream
     << "Usage: " << program << " -E [command] [arguments ...]\n"
     << "Available commands: \n"
-    << "  build build_dir           - build the project in build_dir.\n"
     << "  chdir dir cmd [args]...   - run command in a given directory\n"
     << "  compare_files file1 file2 - check if file1 is same as file2\n"
     << "  copy file destination     - copy file to destination (either file "

Source/cmakemain.cxx

@@ -72,7 +72,7 @@ static const char * cmDocumentationOptions[][3] =
   {"-E", "CMake command mode.",
    "For true platform independence, CMake provides a list of commands "
    "that can be used on all systems. Run with -E help for the usage "
-   "information. Commands available are: build, chdir, compare_files, copy, "
+   "information. Commands available are: chdir, compare_files, copy, "
    "copy_directory, copy_if_different, echo, echo_append, environment, "
    "make_directory, md5sum, remove, remove_directory, rename, tar, time, "
    "touch, touch_nocreate. In addition, some platform specific commands "