kwatchgnupg: Don't modify GnuPG config

The "automatic" modification of the GnuPG config by kwatchgnupg is
unexpected and causes problems (e.g. errors about missing log socket if
kwatchgnupg isn't running anymore). People who want to use the log viewer
should use the GnuPG config editor in Kleopatra to enable logging for
selected components.

Moreover, the watchgnupg executable next to gpg is started instead of a
"random" watchgnupg which happens to be the first one in PATH.

• GnuPG-bug-id: T7259