Remove unused panic handlers (panic-halt)

Declaring panic-halt as a depencency works fine for building the example
code. But it makes 'cargo doc' fail due to the duplicate lang item
'panic_impl'.

Author: sirhcel

src/05-led-roulette/auxiliary/Cargo.toml

@@ -12,5 +12,4 @@ version = "0.2.0"
 cortex-m = "0.6.4"
 cortex-m-rt = "0.6.13"
 stm32f3-discovery = "0.6.0"
-panic-halt = "0.2.0"
 panic-itm = "0.4.2"

src/05-led-roulette/build-it.md

@@ -57,7 +57,6 @@ $ cargo build --target thumbv7em-none-eabihf
    Compiling cfg-if v1.0.0
    Compiling paste v1.0.4
    Compiling stm32f3-discovery v0.6.0
-   Compiling panic-halt v0.2.0
    Compiling embedded-dma v0.1.2
    Compiling volatile-register v0.2.0
    Compiling nb v0.1.3

src/06-hello-world/auxiliary/Cargo.toml

@@ -11,5 +11,4 @@ version = "0.2.0"
 cortex-m = "0.6.4"
 cortex-m-rt = "0.6.13"
 stm32f3-discovery = "0.5.0"
-panic-halt = "0.2.0"
 panic-itm = "0.4.2"

src/07-registers/auxiliary/Cargo.toml

@@ -11,7 +11,6 @@ version = "0.2.0"
 cortex-m = "0.6.4"
 cortex-m-rt = "0.6.13"
 stm32f3-discovery = "0.6.0"
-panic-halt = "0.2.0"
 panic-itm = "0.4.2"
 
 [dependencies.stm32f3]