t0027: tests are not expensive; remove t0025

t0027: tests are not expensive; remove t0025

The purpose of t0027 is to test all CRLF related conversions at "git
checkout" and "git add".  Running t0027 under Git for Windows takes
3-4 minutes, so the whole script had been marked as "EXPENSIVE".

However, the "Git for Windows" fork overrides this since 2014:
"t0027 is marked expensive, but really, for MinGW we want to run
these tests always."

The test seems not to be expensive on other platforms at all: it
takes less than 14 seconds under Linux, and 63 seconds under Mac Os
X, and this is more or less the same with a SSD or a spinning disk.

So let's drop the "EXPENSIVE" prereq.

While at it, retire t0025; recent "stress" tests show that t0025 is
flaky, reported by Lars Schneider <larsxschneider@gmail.com>, but
all tests in t0025 are covered by t0027 already.

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>