Remove paths to fetched TF-M repos from .gitignore

In ARMmbed/mbed-os-tf-m-regression-tests#96
we relocate the path to clone TF-M to a shorter one. This solves
an unsupported long path issue on Windows, and also makes the TF-M
and tests easier for developers to locate. Hence there's no need
to ignore the old path.

Note: For TF-M v1.0, we don't support building them from source
anymore, so it's also been removed from .gitignore.

Author: LDong-Arm

.gitignore

@@ -98,10 +98,6 @@ test_suite.json
 # default delivery dir
 DELIVERY/
 
-# Directory used to clone and build TF-M
-platform/FEATURE_EXPERIMENTAL_API/FEATURE_PSA/TARGET_TFM/TARGET_TFM_V1_0/TARGET_IGNORE/
-platform/FEATURE_EXPERIMENTAL_API/FEATURE_PSA/TARGET_TFM/TARGET_TFM_LATEST/TARGET_IGNORE/
-
 # CMake
 CMakeCache.txt
 cmake_install.cmake