Keep original file if -c or --stdout is given

Set removeSrcFile back to false when -c or --stdout is used to improve
compatibility with gzip(1) behavior.

gzip(1) is removing the original file on compression unless --stdout or
/-c is used. zstd is defaulting to keep the file unless --rm is used or
when it is called via a gzip symlink, in which it is removing by
default. Specifying -c/--stdout turns this behavior off.

programs/zstd.1.md

@@ -212,7 +212,7 @@ the last one takes effect.
     disable input and output checks. Allows overwriting existing files, input
     from console, output to stdout, operating on links, block devices, etc.
 * `-c`, `--stdout`:
-    write to standard output (even if it is the console)
+    write to standard output (even if it is the console); keep original files unchanged.
 * `--[no-]sparse`:
     enable / disable sparse FS support,
     to make files with many zeroes smaller on disk.