etc: removing singular and plural fields from default unitrc.

We forgot to edit the default unitrc when removing these fields in
commit 2a00a9e60a. It's OK since our code can still read these fields
for backward compatibility anyway, but better clean up the file.

etc/unitrc

@@ -9,46 +9,34 @@
    (factor 2.540000)
    (digits 2)
    (symbol "cm")
-   (abbreviation "cm")
-   (singular "centimeter")
-   (plural "centimeters"))
+   (abbreviation "cm"))
 
 (unit-info "meters"
    (factor 0.025400)
    (digits 4)
    (symbol "m")
-   (abbreviation "m")
-   (singular "meter")
-   (plural "meters"))
+   (abbreviation "m"))
 
 (unit-info "feet"
    (factor 0.083333)
    (digits 4)
    (symbol "'")
-   (abbreviation "ft")
-   (singular "foot")
-   (plural "feet"))
+   (abbreviation "ft"))
 
 (unit-info "yards"
    (factor 0.027778)
    (digits 4)
    (symbol "yd")
-   (abbreviation "yd")
-   (singular "yard")
-   (plural "yards"))
+   (abbreviation "yd"))
 
 (unit-info "typogr. points"
    (factor 72.270000)
    (digits 0)
    (symbol "tpt")
-   (abbreviation "tpt")
-   (singular "typogr. point")
-   (plural "typogr. points"))
+   (abbreviation "tpt"))
 
 (unit-info "typogr. picas"
    (factor 6.022500)
    (digits 1)
    (symbol "tpc")
-   (abbreviation "tpc")
-   (singular "typogr. pica")
-   (plural "typogr. picas"))
+   (abbreviation "tpc"))