test: Remove 'error:' from error pattern

May include ansi escape code for color rendering on certain terminal.

src/test/compile-fail/cap-clause-both-copy-and-move.rs

@@ -1,5 +1,5 @@
-// error-pattern:error: Variable 'x' captured more than once
+// error-pattern:Variable 'x' captured more than once
 fn main() {
     let x = 5;
     let y = sendfn[move x; copy x]() -> int { x };
-}
+}

src/test/compile-fail/cap-clause-double-copy.rs

@@ -1,4 +1,4 @@
-// error-pattern:error: Variable 'x' captured more than once
+// error-pattern:Variable 'x' captured more than once
 fn main() {
     let x = 5;
     let y = sendfn[copy x, x]() -> int { x };

src/test/compile-fail/cap-clause-double-move.rs

@@ -1,4 +1,4 @@
-// error-pattern: error: Variable 'x' captured more than once
+// error-pattern:Variable 'x' captured more than once
 fn main() {
     let x = 5;
     let y = sendfn[move x, x]() -> int { x };

src/test/compile-fail/cap-clause-move-upvar.rs

@@ -1,4 +1,4 @@
-// error-pattern: error: Upvars (like 'x') cannot be moved into a closure
+// error-pattern:Upvars (like 'x') cannot be moved into a closure
 fn main() {
     let x = 5;
     let _y = sendfn[move x]() -> int {