syntaxes: remove unneeded backslash escapes before quotes

(They may have been needed in the past to avoid miscoloring of the
nanorc file itself, but they are no longer needed now.)

syntax/autoconf.nanorc

@@ -14,7 +14,7 @@ color cyan "\<[[:upper:]_[:digit:]]+\>"
 color red "\<[-_.0-9]+\>"
 
 # Strings:
-color red "\"[^"]*\""  "\'[^']*\'"
+color red ""[^"]*""  "'[^']*'"
 
 # Backticks:
 color green "`[^`]*`"

syntax/elisp.nanorc

@@ -27,7 +27,7 @@ color brightred "\<(t|nil)\>"
 # Keywords
 color blue ":(\w|[?-])+"
 # Strings
-color yellow start="^[[:blank:]]+\"" end="[^\]\""
+color yellow start="^[[:blank:]]+"" end="[^\]""
 color yellow ""(\\.|[^"])*""
 # Comments
 color cyan "(^|[[:space:]]);.*"

syntax/guile.nanorc

@@ -18,7 +18,7 @@ color brightred "(#t|#f)\>"
 # Keywords
 color blue "#?:(\w|[?-])+"
 # Strings
-color yellow start="^[[:blank:]]+\"" end="[^\]\""
+color yellow start="^[[:blank:]]+"" end="[^\]""
 color yellow ""(\\.|[^"])*""
 # Comments
 color cyan "(^|[[:space:]]);.*"

syntax/json.nanorc

@@ -10,16 +10,16 @@ comment ""
 # Numbers (used as value).
 color green ":[[:space:]]*\-?(0|[1-9][0-9]*)(\.[0-9]+)?([Ee]?[-+]?[0-9]+)?"
 # Values (well, any string).
-color brightmagenta "\".+\""
+color brightmagenta "".+""
 # Hex numbers (used as value).
-color green ":[[:space:]]*\"#[0-9abcdefABCDEF]+\""
+color green ":[[:space:]]*"#[0-9abcdefABCDEF]+""
 # Escapes.
-color green "\\\\" "\\\"" "\\[bfnrt]" "\\u[0-9abcdefABCDEF]{4})"
+color green "\\\\" "\\"" "\\[bfnrt]" "\\u[0-9abcdefABCDEF]{4})"
 # Special words.
 color green "\<(true|false|null)\>"
 
 # Names (very unlikely to contain a quote).
-color brightblue "\"[^"]+\"[[:space:]]*:"
+color brightblue ""[^"]+"[[:space:]]*:"
 
 # Brackets, braces, and separators.
 color brightblue "\[" "\]"

syntax/man.nanorc

@@ -17,7 +17,7 @@ color yellow "^\.(RS|RE|UR|UE|PD|DT)"
 color yellow "^\.(ad|bp|br|ce|de|ds|el|ie|if|fi|ft|hy|ig|in|na|ne|nf|nh|ps|so|sp|ti|tr)"
 
 # Comments.
-color cyan "(^\.)?\\\".*"
+color cyan "(^\.)?\\".*"
 
 # Trailing whitespace.
 color ,green "[[:space:]]+$"

syntax/po.nanorc

@@ -7,7 +7,7 @@ comment "#"
 color green "^#.*$"
 color yellow "Copyright|\(C\)"
 # Header fields.
-color brightred "^\"X-Bugs:.*\"$"
+color brightred "^"X-Bugs:.*"$"
 color brightmagenta "\<(Project-Id-Version|Report-Msgid-Bugs-To|Last-Translator|Language(-Team)?|X-Bugs|X-Generator|Plural-Forms)\>"
 color cyan "\<(POT-Creation-Date|PO-Revision-Date|MIME-Version|Content-Type|Content-Transfer-Encoding)\>"
 # Encodings and numbers.
@@ -21,7 +21,7 @@ color yellow " (no-)?[-[:alpha:]]+-format(,|$)"
 # Format specifiers.
 color brightmagenta "%([1-9]\$)?[a-z]*"
 # Quotes and escaped characters.
-color yellow "\""
+color yellow """
 color cyan "\\([abcefnrtv"\]|x[0-9abcdefABCDEF]{2}|[0-7]{3})"
 # Reminders.
 color brightwhite,yellow "\<(FIXME|TODO|XXX)\>"

syntax/rust.nanorc

@@ -22,10 +22,10 @@ color magenta "[A-Z][A-Z_0-9]+"
 color magenta "[A-Z][A-Za-z0-9]+"
 
 # Strings
-color green "\".*\""
-color green start="\".*\\$" end=".*\""
+color green "".*""
+color green start="".*\\$" end=".*""
 ## NOTE: This isn't accurate, but matching "#{0,} for the end of the string is too liberal.
-color green start="r#+\"" end="\"#+"
+color green start="r#+"" end=""#+"
 
 # Comments
 color blue "//.*"

syntax/xml.nanorc

@@ -12,7 +12,7 @@ color green  start="<" end=">"
 color cyan   "<[^> ]+" ">"
 
 # The strings inside the tag:
-color magenta "\"[^"]*\""
+color magenta ""[^"]*""
 
 # Comments:
 color yellow start="<!DOCTYPE" end="[/]?>"