syntax: perl, ruby: remove arbitrary highlighting of here documents

The rules assume that 'STOP' (for Perl) or EOT (for Ruby) is the
terminating string while it could be anything.  Also, the rules
don't take quotes nor backticks nor a tilde into account.

In short: these coloring rules are far too limited.

References:
  https://perldoc.perl.org/perlop#%3C%3CEOF
  https://docs.ruby-lang.org/en/3.0.0/doc/syntax/literals_rdoc.html#label-Here+Documents+-28heredocs-29

Signed-off-by: Hussam al-Homsi <sawuare@gmail.com>

syntax/perl.nanorc

@@ -20,5 +20,3 @@ color white start="(^use| = new)" end=";"
 
 # Comments.
 color green "(^|[[:blank:]])#.*"
-
-color yellow start="<< 'STOP'" end="STOP"

syntax/ruby.nanorc

@@ -31,7 +31,5 @@ color green "'([^']|(\\'))*'" "%[qw]\{[^}]*\}" "%[qw]\([^)]*\)" "%[qw]<[^>]*>" "
 # Comments.
 color cyan "#[^{].*" "#$"
 color brightcyan "##[^{].*" "##$"
-# "Here" docs.
-color green start="<<-?'?EOT'?" end="^EOT"
 # Some common markers.
 color brightcyan "XXX|TODO|FIXME|\?\?\?"