[string.capacity] Remove parentheses from "reserve()"

It's very confusing to talk about `reserve()` when describing a call to
`reserve(size_type)`, given that the overload `reserve()` also exists.

source/strings.tex

@@ -3009,8 +3009,8 @@
 \effects
 A directive that informs a \tcode{basic_string} of a planned change in size,
 so that the storage allocation can be managed accordingly.
-After
-\tcode{reserve()},
+Following a call to
+\tcode{reserve},
 \tcode{capacity()}
 is greater or equal to the argument of
 \tcode{reserve}
@@ -3019,7 +3019,7 @@
 \tcode{capacity()}
 otherwise.
 Reallocation happens at this point if and only if
-the current capacity is less than the argument of \tcode{reserve()}.
+the current capacity is less than the argument of \tcode{reserve}.
 
 \pnum
 \throws